Both clovers can make an excellant ground cover. The dwarf clover (marsilea minuta) requires less light and and has smaller leaves, while the four leaf clover (marsilea quadrifolia) is much easier to find. With the amount of light you've got, you should have no trouble growing either one.
Most people use fishing twine or nylon mesh to attach riccia to wood or stones. Travis wrote a how to not too long ago on how to do this. I believe it's in the aquascaping forum. With your current lighting usage, you may run into some problems keeping the Riccia alive submersed. If you do, I'd recommend trying a high noon lighting period for a few hours with all of your available light. You may also find that you don't have enough CO2
from the Red Sea kit. You'll need to check your CO2
levels to find out. Test for pH and KH
and compare against one of the CO2
I've read an occational post on how to get stem plants (like Micranthemum umbrosum) to attach to driftwood. From what I've seen this is a much more involved process. You would need to make a pouch filled with substrate and attach this to the driftwood. The stem plant could then root into the pouch. I'm not aware of anyway to have it attach directly to the driftwood.