I have a little Beagle that I have blood trained. I didn't have any blood either so here is what I came up with and it worked awesome!
You will need 3 things:
1: Raw ground venison
2: A old sock you don't plan on using anymore ( I like white because it shows me how well the blood is bleeding into the sock)
3: Some fishing line or string
First thaw out the ground venison to room temp (this will allow it to bleed better)
Next take the raw venison and stick it into the sock.
Next take the fishing line or string and tie the sock shut at the top leaving about 5'-6' of tag to drag the sock.
Now just let the meat bleed into the sock for a few minutes. You can also smush the meat in the sock with your hands to speed up the process.
Next just find you a place to lay down the trail and start dragging the sock around and at the end of the trail leave the sock kind of hidden some place for the dog to find. Obviously when the dog finds it praise the heck out of the dog and I even give mine a hand full of bacon treats.
All the times I have done this it has never left a visual trail of blood so try to remember where you drag the sock so you can tell if the dog is still on the trail or not. I like to try to drag it by visual marks like stumps, trees, etc so I can tell if she is hitting those spots with her nose or not. So far she has been flawless on these trails. Our longest trail to date was probably 3/4ths of a mile in a large city park with all kinds of other dogs and distractions. She was all business and never strayed from the trail. I got lots of funny looks when I was dragging that sock around though.