i dont think so. however, you could cluster all your defensive cooldowns in 1 button, all offensive cooldowns in 1 button, and for abilities like mercy stroke, you could have it under all your main attacks (heavy swing, skull sunder etc) since it is off gbc and that allows mercy stroke to take precedent over your main attacks when it becomes available. just try to be a little creative.

im also surprised you have so little keys to play around with. i have:

1, 2, 3, 4
q, e
alt 1, 2, 3, 4
alt q, w, e, r
alt f1, f2, f3, f4
ctrl 1, 2, 3, 4
shft 1, 2, 3, 4

and they are all quite easy to use!