Sorry but had to create this thread because I found nowhere what I wanted to know and found the way it can be done by accident. I don't know if it is a bug, hidden or a newly implemented feature but it can be achieved quite easily.
All you need to do is go to activity settings (you need to do this for each activity in which you want to view the watch face) and DISABLE the LAP button. Now start the activity and press LAP and voila - your watch face. If you cycle through (as normally with UP and DOWN buttons) all the widgets, it is possible you cut GPS to your activity, but if you just stay on the watch face you are fine. To go back to cycling through the activity screens, just press LAP again.