If you're any good at understanding how to wire something up these guys
can hook you up cheaper than you think.
They built a boost sensitive ignition for a supercharged Valkyrie I built last year. 10 separate advance curves depending on manifold pressure. For under $300 USD and plug in easy to install. Took some dyno time to sort it out but your bike is nowhere near as complicated. After sale support is pretty good if you have patience. Thier English is good but terminology can be confusing.
Contact them and tell them what you're running and they can supply something that will plug in and work.