So I have been wanting to do this for a while and finally got around to it. I have long looked at the I-Mate but never wanted the price for what it did. So I went about hacking up my own interface and here it is!
The button box has memory keys for contesting as well as a PTT button, frequency up and down buttons, and the switch is to disconnect the MIC from my Heil ProSet Plus, I do this because I run my Rigblaster Advantage directly to the rear accessory port so I don't need to mess with things going digital. However using that port opens the mic on the front jack... this was my workaround!
Schematics pulled from the ICOM manual page 18 and 104