Well, if you can physically reach the clip holding the HS to the socket, then no, you don't NEED to remove it.
However, the added room to work, coupled with the knowledge that a screwdriver is much less likely to slip when you're comfortably holding it is worth the added 30 minutes of removing/reinstalling the board into the case.
I have an Antec 1040. Same case, basically. My Epox 8RDA+ mobo angles the HS/Clip in such a way that you pretty much HAVE TO remove the board from the case. A PITA, but worth it to me.