In reply to ross_spours:
Someone else has already mentioned it, but have you tried sticking the removeable tongue depressor further down into the boot to reduce the volume above the foot?
Failing that, try the size you've got, alongside the next size up, both with volume reducing insoles, and maybe look into supportive insoles like Sole, and Superfeet. The shape of the arch should help to give another object to reduce the amount your foot moves forwards. Not to mention give you a more stable platform when walking and climbing.