When you have several exits and are on the free plan with 1 Celpax, participation can be tricky.
I had another HR with a similar situation. We did an experiment with them hanging the Celpax in their HR dept. It was a total flop!
What we learnt from that installation, and from others, is that the participation rate highly depends on where it physically hangs. It has to be easy to press, i.e. on your natural way out.
In one company they went from 9 pulses to 113 the day after moving the Celpax so that it was hanging near the elevator instead.
So now that I'm much wiser (and older hehe) my suggestion would be to look for a volunteer - a manager that's genuinely interested in sitting down and talking with his people about what makes them press green - and start in her/his department with your support. You can then use their experience as you launch to your whole company in August.
I always put some extra stickers in the box that you can use when the time comes to move it.
Have fun creating a better workplace :)