[smileysteve]

It's more hardware intense, but yes, add an rfid tag to each key, use a btle obd dongle, centralize computing in an arduino; phone home to a webserver the last logs.

Then at the end of the month debit each account that used negative gas.

The only thing this misses is encouraging fill-up before empty, but it could give notice when the tank is below ¼ before a trip