Given current market uncertainty and the possibility of near term buying opportunities, either in RE or stocks, I'd just put that money into a MM account. VMFXX is currently paying 1.89%, which is actually more than BND at 1.78%.
Contrary to popular advice, we hold bonds (BND) in our taxable account. Since the reason we own bonds is so that we can spend that money when stocks are down, it doesn't make much sense to me to hold them in a tax deferred account that I'm not yet old enough to access without penalties. Obviously, as OP pointed out, we could sell stocks in our taxable account and then buy them back in one of our tax deferred retirement accounts, but that just seems like an unnecessary extra step to me. The ~$200K in BND in our taxable brokerage account has been paying ~$450/month in "dividends", which automatically gets put into our Vanguard money market account each month and has been providing a nice supplement to our FIRE income.
My thinking is that the money in our tIRAs and Roth IRAs will be the last money we spend, so those accounts are 100% VTI. Since we FIREd in 2016, we haven't paid a penny in federal income taxes, so we're not that worried about a few thousand extra in bond interest income. YMMV.