Is it possible to install Windows 8.1 on a disk with two other OS X versions? I have one partition with Yosemite and another partition with Mountain Lion for some legacy software. But I want to also install Windows 8.1 and use it in dual boot.

Bootcamp is asking me to have only one partition, before installing Windows. Is there any workaround to make Bootcamp think the partition it runs on is the whole disk, or something like that. I don't want to erase my Mt Lion partition then install Windows then, if possible, re-create a new OS X partition for Mt Lion, etc. I actually need the Mt Lion partition to still work. It's weird Apple didn't think you'd ever need more than one partition if you want to install Windows too.
WARNING:

If you create another partition in OS X after installing Windows with Bootcamp, it is very likely your Windows partition will become unbootable. Apparently Bootcamp cannot handle more than 4 partitions: EFI, OS X, Recovery, and Bootcamp/Windows.

Be sure to make backups and be aware of the risk of losing your Windows partition if you create an extra partition in OS X after installing Windows with Bootcamp.