You can modify a grease gun to pump oil , Guy Leutard ( hope i spelt that right !) put out an article called a breif treatise on machine oiling and you get the plans for the oil gun mods.
Basically it is to modify the clip on nozzle but i just welded up the the part that holds the grease cartridge to make it into an oil canister , remove all of the spring plunger unit that pushes on the grease and left the nozzle as set for grease – works for me !
You can get some leakage around the zerk but i find it is minimal and wasn't worth worrying about.
Ian