Sperm plugs have nothing to do with getting a female gravid. I pop the plugs from a lot of my males before putting them with females. Sperm plugs are not viable sperm, just a waste product. The males obviously have to be producing sperm to fertilize the follicles, but the sperm plugs that you see have nothing to do with it. Snakes ejaculate while locked up just like us humans.
On a side note, snakes do not ejaculate like we do. Actually the sperm enters the cloaca from the testes and travel up a groove in the hemipene and into the females cloaca.