Hello, I can definitely help, I am an old 12+ years telco developer, having knowledge from IVR and voicemail systems to ss7/sigtran and lbs. I am actually doing a slir/slia solution for ppl location, although we are working with the operator, we are not deploying any bts in the field.
I see what you're looking for and think I can help, it would be possible to send a hidden sms to enable the mobile attaching to your bts an then having a location inmediately available with an ATI. The location will be with an error of 180 to 1000 meters anyway.
Let me know if you think I can help, I am ready to start discussing your project, I am assuming you're gonna make everything by standards.
regards,
alex