Before you start cutting holes in the a pillar, how about some kick panels? Or, since you say that they sound good under the dash, but the stage is too low, so why not buy an extra set of tweeters and place those up a bit higher. Not extremely expensive ones, just somethng a bit cheaper, but not too cheap. Then place those somewhere a bit higher and set them at a lower volume, or lower gain than the lower tweets. This can help raise the sound stage a bit and still get the good sound stage you were looking for.