Actually, I'm surprised more people don't rhapsodize about specific key sounds, rather than the topre *thock* in general. Spacebar, LCtrl and LShift on the HHKB all have very nice tones.
Don't have an RF in front of me, but I believe it has the same spacebar spring as the HHKB, yes? Probably then, outside of extensive mods, the sound is unrecreatable - it's just a result of the HHKB's odd acoustic factors - the case-mounted switches, the plastic used throughout, the largely hollow case with an off-center controller board...
If your main concern is switching between keyboards, you should get used to it quickly. I find that I'll make about two errant keypresses and then be fine for the rest of the day.