Ya the Check Interact Distance would be the real way to do this. I saw something else in the Gruul_Assist thread that said the C'thun assist used bandages to check distance with others... I was looking all thru the code and didn't see anything about Bandages. I saw it using CheckInteractDistance at one point though.
The C'thun assist used CheckInteractDistance. The new Gruul assist uses bandages.