775 and 1155 aren't compatible (1155 is slightly larger) but if you're cooler is certified 1156 it's ok for 1155 and upcoming 1150 "Haswell"
(i can proove as i myself tried to do this)
There are mixed messages out there on the interweb - like you, some say it can't be done. Others say they've done it (albeit with a small bit of judicious filing). Maybe id depends on the actual cooler.
My motherboard should turn up shortly so I can investigate. Will only set me back a couple of days if I can't. Patience & all that.
Reassuring though to know that my thinking is correct though & that there are no arcane mysteries involved.