Getting my house trained dog to go when and where I want him to

Question
I am the proud owner of a very smart, 19 month old German Shepherd Black Lab X. He is a neutered male and has been for almost a year. He is house trained and knows and understands many basic and intermediate commands such as sit, stay and roll over. I recently moved into a condo(from a house with a big backyard) and he has been "going" on the snow on the balcony. He will not go to the bathroom while on a leash or while we are out walking. I bought a pet potty, which in essence is drain crate with fake sod ontop. I set this out on the balcony. I had big hopes that when the snow melted he would naturally make the progression to the grass like potty. Well the snow is almost gone and now I am cleaning poop up off the cement. I would really like him to use this if at all possible but I don't know how to train him to do so. I had a suggestion to slowly work him up to being on a leash, like put the leash on and stand inside while he goes outside. But he gets too excited as he thinks it is time for a walk. This is unsanitary and I don't know what to do. I am thinking I might have to kennel train him, but I am a student and am in the middle of final exams at the moment. I have had nights where when he asks to be let out I take him out side on his leash, wait for 10 minutes and then go inside, and repeat with no luck. I don't think he likes to be watched. Is there anything you can suggest to do? I don't want to have to leave my dog at our farm if I can avoid it. Thank  you in advance.

Answer
First, I like the idea of you taking him on the leash outdoors (why on earth would you want a dog peeing on your balcony anyway LOL) and repeating the housetraining process.  If he doesn't go, back he goes in his crate (another excellent idea), and repeat, as many times as it takes.
If he has a word that you use, such as "go potty" then use it - every time.  The first time that he goes where you want him to (he eventually should, lest he "explode"), praise him by giving him a food treat (just a millisecond after he's done) and say "good potty" (or good whatever-your-word-is).  This is just a case of the dog having learned to go in one spot on one substrate, and not having generalized that to mean "go anywhere, so long as it's outdoors".
If you continue to have trouble, grab a copy of "Way to Go - How to Housetrain a Dog of Any Age" by Patricia McConnell (Amazon or dogwise.com should have it, and it's relatively inexpensive).  That should help.