Given the conditions already existing, I'm not sure you can do much :-) Kinnikinnick is a great evergreen groundcover for slopes but it doesn't establish very rapidly and it is not ideal for weed suppression.....nor will it ever be. It's growth habit is just a bit too loose and airy to be ideal for that purpose.

Pre-emergents may be your only solution but they will have their drawbacks as well. Amaze would not be my first choice....it's formulation is pretty weak and it is only effective on annual weeds. Preen (not the organic formulation) is better. And you will have to remove any existing weeds first, including the roots of any perennial weeds like dandelions, etc. And reapply the product periodically, especially in fall and early spring when most weed seeds germinate. Mulching will help as well, if at all possible.