I honestly don't know, but I don't see why you couldn't rig up a little switch box.
It's not something I have to mess with on the FT-8800, which has a data port on the back so I never had to use the mic & speaker to connect. My guess is you'll end up unplugging the TT when you want to use the radio for voice.
The keyboard sounds pretty cool, have to let me know how the adapter works. The keyboard I got was something like $1.98 at Microcenter because who still uses PS2 ones? Apparently hams are the only ones. :-)
'91 Pickup - Imelda
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"Our task must be to free ourselves from this prison by widening our circle of compassion to embrace all living creatures and the whole of nature in its beauty. Nobody is able to achieve this completely, but the striving for such achievement is in itself a part of the liberation and a foundation for inner security. " --Albert Einstein