Hmm lol i always push down and twist so it breaks the "seal" the tim creates then i pull the heatsink off works every time for me but i know what u mean i did that on a old Dell once bent one pin but bent it back.
get your rig ready to be dismantled... then do a bit off benchmarking for 30mins, or so, to warm up the CPU and heatsink... this should be amply warm enough to seperate them both