Hello,
I tye my nymphs unweighted, because I also use them in non-moving water which predominates here in Texas.
When I have the good fortune to get on some moving water, I just thread my tippet through a beadhead and let the bead just slide up against the fly. I do this with soft-hackles as well. I usually use gold, silver or black beads.
Cheers,
Richard in Plano Texas