In reply to douwe:
You don't have to go overboard when making wooden holds. Cut up your scrap into vaguely interesting shapes, round the corners and edges a bit, sand to reduce the splinters and screw them directly to the wall.
If you've used cheap ply to build the panels, this often delaminates and splinters when uses as holds but painting first with dilute PVC makes them pretty solid. Stack and arrange them to make more complex shapes.
If you've disposed of your off-cuts get around to a local joiners and ask for a bag of off-cuts - you'll get a lifetime supply of hardwood holds for a fiver.
You can also texture them - I use smear of cement based tile adhesive for a fine grit texture (cheaper and easier than anything else including sand+glue).