John,
That's your definition of a good solution.
Yes, it was. Be careful when you scratch an itch - you'll make that thin skin of yours bleed all over the place. 
Regardless, have you thought about just hooking up a DCS Remote Commander in Passive mode so that when you select a siding with your selector switch, the DCS Commander receiver emits the watchdog signal?
The receiver is less expensive than a TIU and, unlike the TIU, there's no Aux. Power requirement. This solution should be just as simple as yours only less expensive and a bit less work to implement.
BTW, it's on page 206 of The DCS Companion 3rd Edition.
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