I understand completely about "funding" - just be a little careful about pulling too many rabbits out of the hat to escape what needs to be done here to do it right. What we've given you with the FAQ should be looked upon as a temporary getaround for only a "control group" of informed users who understand it's a kludge with limitations and no guarantees and is most certainly not supported by anyone, least of all the manufacturer. Otherwise these bozos will beat you up when there are problems and have you milking that same goat until it dies.
By the way, it would probably be worthwhile to inform the users about the potential peril that can occur from dialing-into your homemade bridge from a cell phone. If they do, all bets are off and you may wind up with echo out the wazoo and about which you will be helpless.
We use this lash up as an "order wire" or whoop-n-holler circuit with a multiline set programmed to auto-answer for our own techs who themselves are telecom pros. Never in my wildest hallucinations would I ever put something like this in the CEO's office without the standard "you're on your own with this" disclaimer.