Rich,
Your solution as actually better, in my opinion, than silver soldering.
You can improve upon it slightly. Unscrew your replacement lug and file a bit of a flat on the threads, just a bit. Apply Canfield flux to the threads (available at Home Depot, etc. used for lead-free solders) and screw it back into the trigger guard until it is lined up exactly the way you want. Now take a propane torch and some silver/tin (lead-free) plumbing and heat up the TG from the side opposite from where the lug screws in until the solder will flow. The solder will flow into the threads and the little flat will lock the lug in place. Clean the residual flux off the part and clean up the joint with a file and you've got a solid, permanent joint!
Best Regards,
JMC