It may be a bit too late for this batch, but the Sausage Source sells a maple cure for hams and sausages, both domestic and wild game.
If you don't mind the cure (sodium nitrite), it might be one way for you to go. The cure would also make things a little safer during smoking and shipping.
And, when you're done with the sausage, you can always make what's left into brine for a maple venison ham!
Given the recipe you're using, you could try just adding maple sugar. Try about 2 Tbsp. of maple sugar (or maybe just a pinch more) in the mix. Most venison sausage recipes I've seen that use maple sugar use about a 2:3 or 3:4 ratio of sugar:salt.
Let us know how it turns out!