I have thought about doing this with one of my Brittany's. I talked to a guy who has trained several dogs and he puts the blood in a mustard bottle and squirts a line on a fairly unobstructed surface, like a drive way, and puts a piece of meat at the end for a reward. After the dog gets used to this routine he starts cutting back on the amount of blood he uses, putting it in drops, and spreading them out a little. He gradually increases the distances and moves to more difficult grassy surfaces until he is able to get them to follow a trail of drops through a heavily foliaged area.
In the beginning he puts them on a fresh trail and as they progress he starts gradually putting them on trails he made an hour earlier until he is putting them on hours/day old trails. He starts them on a leash and works up to longer lines until he is able to turn them loose on a trail. He tries to keep as much blood as he can from his deer kills and freezes it for training purposes, but said you could use cattle or pig blood that you could probably get from a butcher.
Live to Hunt, Hunt to Live.