Yeah it possible... basically all you would need to do is format your HDD to FAT32 (after backing up your games of course), and create a 3-4gb partition depending on what you want. In this partition you would place the entire wiiflow folder you see on the root of your sd card, and the wiiflow folder in the apps folder on the root of your sd card so it should look like this:
sd root > WIIFLOW > covers (covers go in here) *there will be other folders such as "music" in there as well
apps > wiiflow > .dol file
In the other partition of the HDD you'll put your games just as usual.
Hope I didnt lose you