When you create a new Hyper-V virtual machine, configured with Dynamic Memory, the advantage is to boot a virtual server with minimal RAM allocated (e.g. 512 MB), but the catch is some setups check that the computer it's being installed on has enough memory. I recently was disappointed to see that this same issue / inconvenience exists as I was running through the VMM setup for 2012 SP1 (CTP2). I tried Aidan's tip of using Paint, but I could not get paint to use enough memory, so that the setup prerequisites would let me get by.
Fortunately, I found a post from 2008 on the Windows SDK blog that mentioned tcpanalyzer.exe and consume.exe as "hidden gems" in the SDK. Consume.exe sounded promising, so I went to fetch the latest Windows SDK. Fortunately, consume.exe is still there.
Consume.exe is all of 21KB, so I copied into my newly minted Hyper-V VM (for more on my favorite way to load up a new Windows Server 2012 VM, see … ) and ran consume.exe -physical-memory -time 60.
The 'Assigned Memory' value in my Hyper-V Manager window climbed up above the 2GB (2242 MB) I needed to proceed, and I was able to finish my setup.