While developing a custom firmware for the keypad, I came up with three more possible functions.
The first is a review of the Quick Tune. Rather than sending a carrier for 5 seconds, the operator controls the duration. One key press sets the radio in FM mode and TX, then another key press returns your trusty Yaesu back to the original mode, in RX. This allows to have shorter and longer tuning times. Let's call it Manual Tune.
In between this new function and the original 5 seconds Quick Tune, lies Timed Tuning. 15 levels of delay are preset, so you can chose whether to tune for 1 second, 2s, 5s ... up to 15 seconds. It requires two key presses.
Finally, the Lazy PTT is for heavy ragchewers , those operators that speak for minutes before listening back for comments. Press a button, your radio goes into TX. Press again and the PTT is electronically released. No timeout, so watch out! This is a good substitute to VOX operation.
These functions should work on 817, 857 and 897.