What I do is smear a cheap water based gel on the lace from the underside, just enough that it starts to seep through and pin to mannequin head. Then color the hair with a comb and then finally with an artists brush I get as close to the lace as possible. That last part is the trickiest because if you don't get the dye down far enough it will look like you have blonde roots growing through. I've done this with entire pieces and never stained the lace.