I've never done it, but you should be able to do some sort of directory junction. Since I've not tried it you should probably just do a few Google searches to figure out the best way, but you should be able to....
Stop the Recorded TV HD Service
Move this directory C:\Users\Public\RecordedTVHD to your RamDisk.
Create the correct type of junction/link so that C:\Users\Public\RecordedTVHD points to the new location.
Start the service back up.
I did pretty much did what was recommended. I copied the RecordedHDTV directory to my Ramdisk in my case R:\ and then deleted the copy on my C:\ drive then called mklink /j RecordedHDTV R:\RecordedHDTV from a cmd window in the original directory.Nothing broke by doing this and I think it appears a little quicker. I am still not content with the loading times of the options (recorded on date, type, .etc) but haven't had time to look into this further.Also when I have live TV playing in the background things are still sluggish navigating menu's.