I saw a Chevy 350 video of a guy who took an old points style distributor with a flat headed end and put it in the oil pump hole. He then plugged the oil pressure hole with a oil pressure sending unit and then hand cranked the distributor to get oil to overflow from the lifters to the valley pan.

I was wondering if there is a similar technique for doing that on the 3800, since the oil pump is driven by the gear connected to the crank on the front cover.

I believe GM does have a special tool that connects to the oil pressure sending unit hole. This tool pre lubes the entire engine prior to starting.

The other way(which I have been seeing on other forums is) turn off the fuel system, remove all the spark plugs and turn the engine over for a few seconds. Wait a few, turn it over again for say 10 seconds again. Or at least until you see your OP gauge come up to normal. Reconnect everything and do a live fire.