I don't run conventional so I'm not totally sure about this... but why not just power the TIU from the aux port, and then when you want to run conventional, vary the voltage input to the TIU inputs with the throttle? Then when you want to run DCS, just push the throttle up to 18V and have at it with the remote.
As long as you are using a pure sine wave transformer (ZW, VW, KW, TW, Z, 30B etc.) this should work I think.