adding oil to ac/compressor without discharging
 

is this feasible with an r4? If I filled the lines with some oil before hooking up my gauge set - would that work?

I had a spill mishap when originally installing my compressor last year and I've always felt I'm an ounce or two low on oil.

Let sleeping dogs lie. You're better off with slightly too little oil than slightly too much. Liquids don't compress and you don't want the coils oil-logged. If you had a problem with oiling, you'd know it by now.