I'm probably not too far from a solution, but could someone confirm how the Apache should be configured so that if a domain name is pointed by DNS on the machine, the Apache serves a default "domain parked" page if no Virtual Host is configured for that domain ?
Does it boil down to putting a VH directive telling to serve that "parked" page with the name dynamically inserted in it after all the other VH down the list ?

thanks,

If Apache can't find a specific virtual host, it'll use the first one in the list. So just set up your first VH as a parking page (servername isn't required).

Oh, 1st from the start, that's what I was missing, thank for the help !