Yep, shielded wire is the only way..
I also spoke with Van's about this guage jumping, drive you crazy issue...They DO have the "get used to it" mentality. I on the other hand got vveerrryyy tired of seeing needles jump violently like that and explaing to passengers about the crappy guages. I fixed it on my friend's 6 with shielded wire. Get yourself some stout 18 guage shielded wire to run EVERY (except the ground wire of course!) wire to both the MP and RPM guages. Ground the sheilding at BOTH ends, and leave as little unshielded wire as possible. Even after all this, the MP guage still twitched a little bit at the key of the mike, and this was fixed by wrapping heavy aluminum foil around the guage and grounding the foil! Wow, sensitive little things, huh?
Glen