It seams you didn't get his question: He is NOT asking for the switching feature, just the usage of the "ATI Catalyst" driver, which is certainly possible!
Even with an active Intel IGP (not disabled in BIOS) it is possible, but might need some adjustment. With adjustment I mean, you have to tell the kernel explicitly not to initialize the Intel IGP, which I would try to do in the first place by blacklist the intel kernel module.
I had this configuration (Intel IGP + ATI discrete, both active in BIOS) in my Thinkpad T500 and was running the Catalyst driver. Nowadays I only have the ATI active and the Intel disabled in BIOS, since the Intel useless is in this configuration and might even consume some power.