I do glitter fades with gels all the time...
heres how I do it....
I mix the glitters with gel usually 2 colours..
then after applying bonder gel layer place a stripe of the first colour glitter gel onto the stress area
then do the same with the 2nd colour in zone 1
I then use a dotting tool to pull some of the gel from the stress area down towards the cuticle (I don`t take the glitter right down to the cuticle just slightly above so I don`t file the glitter away when filing the gel flush)
then do the same with the gel in zone 1 but pulling it through the 2nd glitter colour to mix them and create the fade
then use clear gel over the glitter to build apex etc and finish as usual HTH
Hope this makes sense I`m rubbish at explaining things