Hrm. As it stands now, not easily. The RC2HL has the switch flip option in 5-chan mode, though you do have to flip it before or after the TK-RX1x board begins startup (it ignores the switch during startup to try and prevent an "out-of-sync" condition.
Auto-shutoff like the Tamiya units can be iffy if your radio signal isn't good (and the TK-RX1x board takes longer to startup than the DMD/MF), plus it doesn't work with PCM/2.4ghz radios.

I had thought about allowing the user to shutdown the TK-RX board *and* DBC using the key button, but it's tricky, as the DBC has no way of knowing if the TK-RX board is on or off, so it's virtually impossible to keep the two in sync perfectly. I suppose I could at least modify the DBC-HL to not accept hits when the radio is off. That way you could shutdown the TK-RX board, then turn off the radio to disable battling. Only issue might be if the RX then becomes susceptible to noise, which could randomly startup the tank and start driving it! :P
I'll have to take a look and see if I can fit it in, as the PIC is pretty much full right now.

And if you can't trust the other players...I don't know if there's much point in playing with them. They could be spraying the inside of their TBU/DBU with dullcoat on the mirror...added a more powerful IR LED, etc. That said, you could tap the destroy sound output on the RC2HL to drive a FET, which would drive a latching relay to shutoff the tank. As YHR said, you might need a 555 timer in there to delay it enough so that the sound would finish.

D.