How do I get my puppy to pee outside?

The title is a (tiny bit) misleading. Because at home(and when we visited my mom) Albus quickly learned where his toilet is outside, and goes when I put him there. He is a 12 week old Cairn Terrier puppy. At home we're currently working on the cue "peepee" to see if this will help at all.

But I've gone back to work, and he is coming with me until he is about 5 months of age. The problem now - is that I can't get him to pee outside when we're at work. We follow is regular schedule with water and then a trip outside around noon, but he doesn't go at all! This morning he took a number two right outside my workplace, but no pee. However, he doesn't go inside either. In sheer desperation I took him to the toilet of my office to allow him a controlled accident, but he holds it until we get back to his normal spot outside my flat.

Aside from his two spots at my flat, and at my mom's, and the accidents he's had indoor, he has only ever peed elsewhere thrice. Once on grass, and twice on asphalt. I've had him for a month, and when I first got him, he got into the routine of peeing outside within a week. And at my mom's place it only took him a day.

My flat is located on a high street, but I work in the city center, and I get the feeling he gets distracted, but there are literally NO quiet places around. I signal to people not to approach him, but I have no idea what else to do.

We clicker train, and I always throw him a puppy party when he goes. When he goes outside his regular spots he gets several treats to show him how pleased I am.

Have any of you been through the same? I've tried a pee spray that obviously didn't work(but hey - had to try it right?). We're near the end of week one, and I know I may be rushing things, but he's belly gets hard, and I cannot imagine the discomfort he experiences. I just want him to feel comfortable. We've tried the back alley, but there is a dog living in one of the flats, and it barks at him, and he barks back. So I've completely given up on that.