In reply to pasbury:
In addition to those already mentioned, there's the following. I've done all of them, mostly on my tod. All are a bit "off list/ left of centre" so may meet your requirements. You probably wouldn't see a soul on most (all?) of them.
*Yr Wyddfa - Great Couloir of Cwm Tregalan. (Can't really get more off piste than that ....) Loop back via Yr Wyddfa and Lliwedd.
*Tryfan - Bastow Buttress Variant or Nor' Nor' Buttress Variant. Both equally good. Then continue on to summit and lots of people, followed by Bristly Ridge?
*Glyder Fach - Bryant's Gully. Feels a bit committing in places, but is basically ok. Excellent and unusual way of getting to the top of Glyder Fach. Descend to Nant Peris from Glyder Fawr or loop north and descend the Pass.
*Crib y Ddysgl - Llechog Buttress. Excellent. Continue to the summit on the Llanberis path and yet more people, then leave the crowds behind and descend Cwm Glas Ridge back into Cwm Glas.
*Mynydd Mawr - Sentries Ridge. Finish by continuing to the summit.
*Cwm Silyn - Craig Fawr Rib. A road less travelled. Very good though, but it might feel more like a proper Mod rock climb in places.
If I was mean I'd also recommend the Wrinkled Tower on Tryfan, but I won't. You'd probably have it all to yourself though. If you're ever tempted, be prepared as at one point on this sandbag of a scramble you will be faced with a very exciting and exposed move, the sort of move which leads to a brief meditation on life and how it might shortly be coming to an end.
All the above are in Ashton's book.