First, couple of things to consider:
- A SSD has been shown to generally provides similar loading times than a RAM drive in practice (source), even though in theory a RAM drive is faster than a SSD in theory. Also, a SSD would make other things faster, from loading DirectX and other drivers, in addition to game files themselves.
- If you make your RAM disk too large, you may prevent Windows from improving the loading times with caching data on your unused RAM.
- If you make your RAM disk too large, you may induce pagefile swapping, severely slowing things down.
- Since you won't be able to copy the entire game, it will be hard to effectively determine which files are most often used and slowing down the most.
That said, to try doing this, you can use symbolic links (junctions, for folders) to make some files or folders from you Skyrim installation point to the RAM drive locations instead.
- Create a ram drive using one of free softwares available online. Some benchmarks and prices here. I personally like ImDisk because you can create an ISO image of your RAM disk with your files for easier loading the next time.
- Copy a folder or some files, such as the HighResTexturePack**.bsa to the RAM drive
- Move those files from the Skyrim installation folder somewhere else temporarily on your HDD (to restore them later)
Open command prompt as an administrator, and create links for each files to the RAM drive location, using mklink. mklink /h for a "hard" link (so the game can't tell the difference) and /d for a folder link (junction). For example, if R is your ram disk, those examples link one file or one folder.
mklink /h C:\Skyrim\Data\BigFile01.bsa R:\BigFile01.bsa
mklink /d C:\Skyrim\Data\Textures R:\Textures
Play the game.