QuicKeys and Tempo seem to coexist, though I haven't pushed my luck. The PostEvent command needs to know which one you're using, and uses the following rules:
1. If you call PostEvent with only one argument, then it's a QuicKeys sequence or
click name.
2. If you call with 2 arguments, PostEvent checks for a Hypercard global variable
called "Macro". If this global contains the string "Tempo", then Tempo's used. If
the global doesn't exist, or holds some other name, then QuicKeys is used.
Putting the following handler in the card script should be sufficient: