I asked my Rosh Kollel and he told me I should use wine. I don’t really buy anything by the case so I don’t have anything that has kedushas shvi’is. I don’t even think that I ever did anyway.
kapusta
I believe the actual segulah for having the havdalah cup overflow (don’t know what its for anymore) is to have it spill onto the floor.
Unfortunately though, thats also a segulah for bad shalom bayis.