Turns out that you can pop a normal (non-rechargeable) CR2032 in the K750 to replace the rechargeable ML2032 that's already in there. Pretty decent chance of a CR2032 being at the hotel front desk or at the corner store. However, if you do that, it's important that you disable the solar-recharge feature, perhaps by taping over the solar cells.

After having my K750 for about three years, the ML2032 stopped accepting a charge, which made the keyboard nonfunctional. I did the ML2032->CR2032 replacement, put black tape over the solar cells, and the K750 came back to life. That was about a year ago with 8+ hours per day of use, and the CR2032 is still going strong.