Hi, I think this will depend on your hosting account more than your web-builder account. Most people who use the likes of Wix and Weebley are unlikely to have their own hosting package? I must admit I've not heard of site.pro so not sure on their set-up. Assuming you have domain settings controls (and would point said domain to site.pro?) you could possibly set Mach up in a folder within your hosting package, and point a sub-domain at that (mach.yourdomain.com), as certainly in my 1&1 CP, I can set up sub-domains to point to different folders so have several Mach instances on my root folder structure each reached though a sub-domain.
The other way if you have root access, is to add a sub folder (I do this a lot with wordpress installs) so I go to clientdomin.com/MF to get to the MF CP for that client, with the MF folder sitting in the Wordpress install structure alongside the default WP folders. This also helps with client isolation and if they ever take the web management elsewhere, I can simply delete / copy the complete folder as required. Using sub domains isn't as neat but might be needed if you don't have root access to the folder where the website is (as you wouldn't with wix et al)