Here's something to try. Locate some beef suet in your local supermarket. This the big hard chunk suet. Freeze it. After coarse grinding your deer meat use a cheese grater and grate the suet into the burger. I use about 1 lb of suet to 10 lb of meat. Then re-grind using the finer grinder plate. I did some for a buddy in Michigan last month and now the whole town is doing it. Give it a try and let me know how you liked it.
How do you put the bacon into the burger, raw? Do you freeze it and grate it into the burger? Does the bacon cook if it's raw and mixed in when making a burger? I like bacon cheeseburgers but usually cook it separate and add on top.