I worked at a rather hellish job at the Waterfront for a time and there is no easy way to ride there.
You can take the Southside trail to the end and ride the railroad ballast to the Sandcastle parking lot. Sometimes it's open, sometimes not. Sometimes you can ride through it fine, sometimes a big dude with a moustache will get in your face and threaten you with arrest. Otherwise you can take the broken stairs to Rt 837 and ride in the glass filled gutter to the Waterfront.
Or you can go through Squirrel Hill and down the gient hill across the high level bridge. Watch out for traffic, glass, human sized potholes and tons of debris on the road after it rains. The sidewalk is no better as it is filled with debris as well and has driveways on it every 20 yards or so.
Not to be discouraging, just sayin' that getting to Homestead on a daily basis was not enjoyable in the least.