Stu that is one hell of a commute.
The other side of Carnegie is typical ex-urban. More pleasant than Carberry township, but still nto great. ("Carberry" was a typo, but I'll keep it.)
Oscar Swan's Book has a couple rides that might help. Miller's Run and Washington Pike ("The point of the Washington Pike ride is to avoid Washington Pike").
I've done Miller's Run on a Sunday and most of it seemed like it might be OK during a weekday.
You might want to see what Google bike directions give you - most likely not the best route, but some ideas all the same.
PennDOT Bike Route A goes very close to there.
ftp://ftp.dot.state.pa.us/public/pdf/bikes/state_mapA.pdf
http://www.dot.state.pa.us/bike/web/tour_routes.htm
Washington County public transportation. I know Westmoreland Co. has commuter buses that come to Pittsburgh, I'm guessing Washington Co. does too. You might consider buying a foldy.
The hotels at Southpointe have buses to the airport, you might make a deal with one of the hotels.