Maybe you could cut out your stock boost gauge and put the boost gauge there. There's a VFAQ on a custom power mirror cover gauge pod but it might still be recognized. I've been looking and I still haven't found any good stock points, makes me envy the mkiv supras that have a 52mm clock...

I have my boost gauge in a double gauge pod I cut down to make single gauge. I have it mounted almost all the way down the a pillar. It doesn't block my view like the dual gauge did and it's hard to see from the side. It's not perfect but it's the best I can do at the moment.