There is a wide variety of "spouse not on board" situations. In order of severity:
1) spouse is a spendthrift, resists basic saving steps like 401k matches, and will destroy any savings the couple accumulates.
2) spouse is willing to save "normal" amounts like 5-10% and get the 401k match, but likes their SUV/truck, fancy house, expensive hobbies, treats, and luxuries.
3) spouse has frugal tendencies, but either loves the idea of working until 70 or thinks FIRE is a pipe dream / is unconvinced by math.
4) spouse is somewhat frugal, but apathetic about active pursuit of FIRE and unwilling to sacrifice anything at all for it.
As weirdos pursuing FIRE, we must acknowledge that we are the ones expecting something abnormal from our spouses. Many of us got married before the idea of FIRE entered our heads, so we are the ones changing the deal in terms of lifestyle expectations. Our spouses might have 99 good qualities and pursuit of FIRE is the one we have to work on. Some sympathy and understanding is due
In the case of situations 1 & 2, the choices are to give up OR negotiate one's own retirement. This is complicated, because these luxury-addicted personalities see money as only having the purpose of being spent and may come to resent any stash that they can't spend because it's "yours". Suggesting separate finances may also cause them to think you are slow-divorcing. Counseling is recommended. Keep in mind that you probably resent your spouse for their spending, so you'll do a crappy job negotiating.
In situations 3 & 4, the choices are:
a) Do passive things like getting their 401k contributions maxed out, automate savings, and cancel a few credit cards. You let them know of course. (Funny story - my apathetic DW was in her work's payroll portal looking up her schedule. I asked if I could see the keyboard and mouse while she took a phone call. I went to the 401k deduction and maxed it out right in front of her. Then I said, "this will improve our financial security during retirement," she looked and nodded - maybe to the person on the phone, IDK. Clicked save. That was $100k in savings ago.)
b) Get them excited about some tangible results, like saving your first $100k or hitting $250k net worth. Make these milestones celebrations with champagne, roses, beer, whatever they like. Apply classical conditioning: milestones mean we do something fun.
Very wise post. For sure I didn't have the FIRE dream in mind when we married, and when I first started bringing it up, it was not met with acceptance at all. Over time, I've slowly and steadily beat the drum and hammered the message home. Specifically, "honey, I'm 7 years older than you, and I've got a finite window of time to do the very physical things* I love to do and which bring me fulfillment, and I've worked my ass off to give us a good life and put us in the situation where we can both retire early, albeit in staggered fashion. I've got enough between my pension, savings, and future Social Security to (a) replace my share of household income when I retire, (b) and cover your shortfall when you retire (and oh, by the way, I've got enough for us both to retire at the same time if you'd ratchet down your spendy lifestyle)."
This is the gist of the message I've been sending. In addition, I've done the things ChpBstrd mentioned above re: getting her to save more and tracking it and updating her, and celebrating milestones. As she's watched the accounts grow, and at the same time, as she's learned of her friends' dearth of savings or the level of their debt, she's come to appreciate my mindset and is grateful for the abundance we have. Only thing is, now and again, we'll discuss a purchase or the like, and she'll say, "stop being cheap, we have plenty of money!" At which point I have to remind her of why exactly that's the case.
In short, I'll be retiring next year, likely some 5-7 years before she will, and she's okay with it. However, she does (rightfully so given my wanderlust) have concerns about me taking off for weeks at a time while she's going to work every day. I'm working on that.
But to the original post -- I don't like being told what to do, so if it came down to a spouse thinking she could tell me I can't do x or y, well, that shit's not gonna fly, and I'd be hitting the road. I'm in a position now where if I had to give up half my shit, I could still live a nice life on half. That gives me peace of mind.
* rock/ice climbing, backcountry snowboarding, surfing, hiking, camping, etc.