Your answer is contained in your post. You must prevent the dog from leaving the room where you are when he is not crated.

You can do this by using baby gates, or by tethering the dog to your waist with a leash.

In this way you prevent the dog ANY opportunity to urinate without your knowing it.

At the same time, strengthen the dog's interest in outdoor elimination by going with him each time, and rewarding him with a very tasty treat, and plenty of verbal and physical praise. At the time time you are going with him out side, you can train him to urinate on a verbal command. Decide what you wish to use as a command to urinate, and say this in a pleasant tone of voice while the dog is urinating, or just as you see him lift his leg. (I say "go pee pee" to my dogs). If you do this each time the dog is about to urinate, and then food reward him as soon as he is done urinating, he will quickly learn that to urinate when you ask him to gets him a cookie. Very handy when traveling or in the rain, etc. At the same time he is learning it is valuable to him to urinate outdoors.

I would plan to keep this dog from ANY unsupervised house roaming, and to reward outdoor elimination as often as you can, for at least 6 months before you try him for any free time in the house at all.