I didn't know you were living in Montpellier since I read your introduction !
It seems like people from Montpellier really want to select multiple from map
Looking for some partial answers, I found this discussion to create options to select from a repeat group. You'll have to estimate the max number of facilities users wil plot...
I imagine, as in the given example, dynamically populate the geometry column of the choices list...
You use case could also be another scenario for this discussion :
