There are a couple of oil pressure ports that are plugged on the SV engine. I don't remember where they are exactly. Knowing the thread size you could go to an industrial gauge supplier and buy a direct mount gauge. If you were brave and industrious you could plumb up a line and mount the gauge up top.
I think it would be of limited use, given the SV's proven reliability and long lifeline.
Pressure gauge or temp guage? Unless the whole crankcase were filled woth pressurized oil (!) I can't see how it would work. Screw in oil temp guages were common back when SOHC CB750s roamed the earth.
At risk of sounding like a total chump here. I just really thought it looked cool. Plus I have a total analog guage fetish.
I'm using my 03 for performance mods only and my 02 is just a communter. So I figure adding little look only things to it makes since.
If you go with a conventional gauge the sender usually just screws in where the oil pressure switch goes (and replaces it, unless you add a 'T'). If you do buy a gauge, get an electric one, and a good one (AutoMeter etc) IME, (is that a legit abbreviation? In My Experience) the cheap guages don't survive long on a bike.
Also, If we're talking about a 2nd gen bike you may have additional options since you have an oil cooler (plumbing for this may occupy the ports andyauger referred to).