BlueHouse: Thanks, that's great advice. I'm also going to enlist my company's HR department to help me figure this out -- squeaky wheel, etc. It seems like if this is a pretty standard financial maneuver, my company ought to offer a plan that allows it.
MustacheAndaHalf: Yikes, I hadn't fully appreciated the tax math you've pointed out. I also realize I'm probably exposing myself to a higher tax bill than necessary. A couple years ago, I found out my employer offered a Roth 401(k) -- I was doing traditional at the time. Given my age (42) and the fact that I had a decent amount in my traditional 401(k), I switched over and did the full $18K per year in Roth, my thinking being that that way, when I retire, I'll have a nice balance of Roth and traditional money to draw on. I figured I'd draw on the traditional funds right up to the point that income taxes kicked in, and then take Roth $$ if I need more. But the problem, I'm now realizing, is that going full-Roth right now exposed that extra $18K a year to income tax, and I'm in the 33% bracket (plus another 6% state tax). I'm almost certain my tax rate will be lower in retirement, as I won't have mortgage/tuition payments. So I think I may switch the 401(k) back to traditional, and maybe take another look at my wife's 401(k) plan -- it's absolutely terrible; no match, absurdly high fees. But it'd shelter an additional $18K from taxes (more with state tax), and I could roll it over to a Vanguard IRA when she leaves the job at some undetermined point in the future. While it doesn't save my taxes on the front end, I guess I could also pour that extra money into my kids' 529 accounts, too.