Another point to bear in mind here is flow... so for example, fishing the thames in summer (when it resembles a long, narrow barely-moving lake) I'd be quite happy to ball in groundbait (frozen or not) with some form of crumb as a carrier for the hemp/ caster/ mini-pellet/ corn etc that I want to get out as loose feed.
However, switch to a river like the thames in winter or the wye (or as I understand it, the trent or severn with a bit of water on) and throwing anything in to the river would bother me in terms of accuracy - and I'd be back to the feeder cast to a clip as others have suggested.
In fact at the start of the session, I'll often mix up a small batch of dry-ish groundbait which I'll then use to plug either end of a feeder full or hemp or casters or pellets or corn (or better still a mix of all of em...) I'll then use a homemade feeder that I have that is really big but not weighted particularly heavily (about 0.5 ounce of lead). So fully loaded, it's proabably more like 2 or 3 ounces... after I've cast it to the clip, I'll hold the line with my left hand and keep the rod tip in the air... and because the groundbait is on the dry-ish side, it doesn't take long at all before it "pops" and all of the bait comes out. And when that happens, the feeder no longer has the weight to hold the bottom and it will start to more, which you'll feel through the line that you're holding. If you get the groundbait mix just so, this happens about 20 seconds after you've cast, so you can reel in and get another one out. Because the feeder is so large, you can get a good bit of bait out in just 10 or 15 minutes, and you can be confident that it's landing in just the right spot.