You can use an "engine pre-oiler". This device is used by professional
engine rebuilders. You can probably borrow/rent this locally. Basically,
it is a pressurized container containing 1-4 qts of motor oil and is
connected to the block at the oil pressure sending unit port. After
ensuring a good seal, a valve is opened which charges the entire
lubrication system. I borrowed one from the engine rebuilder for my
car (1500 Midget) and it worked great. Hope this helps.
'78 Midget "Betsy"
San Antonio, Texas