If you need hands free, you just need release the bow (free action) and hold it other hand while casting the spell with your now free hand. Imagine someone hold bow one hand, wave hand and chant and then free action draw quiver and place it on bow and fire.<br/><br/>Same deal if your wizard who wields 2h sword; you can place sword tip down temporally and hold it up with one hand while weaving spell with free one hand. Ofc burning hands spell would be harder to pull off with arrow unless firing the bow replaces somatic components of the spell (and most GM's could allow it with arcane archer).<br/><br/>edit; Aye, what EFA said :)