You can bleed with the engine off just fine. For what it is worth I fought the two pump gremlin on my 88" S3 for a few months after replacing the springs. Had new master and slaves on all four wheels andbthe brakes were perfect until the spring change. I finally isolated which wheel was the issue by clamping brake lines until I had a firm pedal. Turned out a fairly new slave had failed. Try clamping to isolated the problem. Also make sure all the bleed nipples are tight.
1995 NAS D-90 Soft Top, AA Yellow
1973 Series III '88 Hard Top, Limestone
1957 Series I, Deep bronze green