I believe you will always be using absolutely more quads than hams, but you CAN emphasize the hams relatively more by changing your seat position. Moving forward a bit, like on a tri bike, will allow you to recruit more hams and glutes.

Of course, you need to be mindful of your knees when fiddling too much with your seat fore-aft position. You might start just by trying to slide forward on your seat when climbing, etc, and see how that feels. If you think it makes sense to try something more and your LBS is generous about fit tweaks, you might have them set you up on a trainer and gradually move your seat forward a bit.