There is a plastic nipple/hose barb on the intake manifold underneath the ECU that you must drill through to connect your boost/vacuum line. As for where to mount your gauge there are many options. There is a trick mounting cup on ebay from the states that clips onto the underside of your steering. Not cheap tho.
Check it out http://cgi.ebay.com/ebaymotors/SEADO...rcraftQ5fParts
The best way is a block-off cap on the end of the manifold, and take from there, as the one you said is a bit biased to that cylinder.
Don't drill, as you can finish up with bits of plastic in the inlet. Just use a hot/heated small rod.. that way no crumbs will get in the manifold.
Or, if its a ski with the fogging tube, you could try this. I have to admit I haven't, but cant see why it will not work.
Just be careful if you use it to tune/set RRFPR though, as its before the butterfly.