If I understand correctly, the Rapid7 scanner is a cloud based vulnerability scanner that you're wanting to use to scan your endpoints?
If yes, you can look at using inbound firewall rules. You need to open a case with Meraki support to enable this feature.
However I feel like a more elegant solution would be to use an on premise proxy to do the scanning and report results to the cloud. I'm thinking similar to how Tenable IO and Nessus scanners work. I'm not sure whether that's a solution provided by Rapid7.