I suppose you could set your ripping program to rip directly to a memory card instead of your computer’s hard drive, but I believe 1.) the ripping process utlilizes the RAM (temporary memory) in your computer during the ‘reading’ process before it actually ‘writes’ it to the hard drive, and 2.) it would most likely be a much slower process to rip it directly to the card.
Additionally, ripping progams (if the computer is connected to the internet while ripping), will draw from online databases to create and fill in the ID3 tags of the music files. These are not always correct, therefore the tags should be checked and/or edited using a program such as MP3Tag so that whatever player you are using will sort and display the meta data (Artist, Album, Track # & Name, etc.) of the songs correctly. This is always best done on the computer. Sometimes the changes don’t ‘stick’ if edited on a player or memory card.
Given all this, I think it’s probably best to rip them to your computer first, then copy the files to the card.