Heated glass bed

Having procurred a piece of 3mm glass, to replace my current CTC bed, I have determined that there is insufficient clearance between the hot end and aluminium bed to attach my glass. I have pushed the hot ends back to the extruder as far as they would go and have adjusted the bed to its maximum distance from the hot end, but there is still not enough clearance. I would guess its circa 2mm gap. Should I just ditch the aluminium bed or am I missing a trick here?

Moderator note: Late posting is due to unexpected delay in obtaining moderator approval

To put a glass bed on you then need to print out a shim the same size as the glass to go in the z-axis, for 3mm glass something like this is what you need http://www.thingiverse.com/thing:1474097