Clematis don't mind being buried a bit. In fact, the advice when planting is to plant them deeper than they were to encourage more buds to form stems. The advice when planting new roses is to bury the graft join a couple of inches below soil level so they won't mind a mulch or compost either.
I have a friend who mulches his entire garden with a couple of inches or more of well rotted compost every winter and his plants all come through just fine - 2 care garden with trees, shrubs, roses, clematis, perennials and bulbs. The reasoning is that the worms will work it in to his heavy clay soil and gradually improve it and it works.
I would just get in there asap and put up some trellis or wire supports for the clematis before everything starts to shoot. Roses can be pruned now if you have mild winters but not when a frost is forecast as this damages the fresh wounds and can introduce disease. It's also OK to wait till March if you have cold winters.