Switchgrass is pretty easy. Its seed is smooth and it will run through any small seed box found on most drills. Indiangrass is a little trickier. It has a hairy seed that really does well in a fluffy seed box designed for native warm season grasses. Lots of counties agencies rent drills (cheap, $10/acre here) that have native warm season grass capability.
They are cost prohibitive for most people to purchase, figure 15k for a small drill with all three (main, small, fluffy) seed boxes. I have a drill I use for food plots with a small seed box and a main box that cost me near 10k used.
You said you didn't want a drill, but I want to encourage you to reconsider. If you really can not find a drill for some reason, you can get fair results mixing indiangrass seed with sand or kitty litter through a broadcast spreader. The seed cost is high enough that the drill rental will end up cheaper if rental is a possibility.
Switchgrass can be frost seeded with good results. Not sure about indiangrass, maybe a cultipacker?