Can I Effectively Jump my Furnace Wiring for A Long Time Safely
Can this be jumped safely, YES. Many furnace controls have the fan only option but as you found the wires did not extend to the thermostat. If you were able to use the 24v to pull in the fan relay and not activate the gas valve what you have done would not be a problem with normal low voltage thermostat wiring and would be hard to be unsafe at 24v.

Prior to installing any wiring I would get permission from the land lord. 
 I have installed toggle switches on furnaces in the past for this same reason, to have a fan option, I did not consider pulling new 5/7 conductor wire to the thermostat as that would have doubled the cost of the job. The furnace was conveniently located, so it was no big deal to just flip the switch.