Hello,
I run a lot of mojoPortal websites and the majority of them use more than 50MB. You can try it but more than likely you will run into problems because the app pool will recycle when it grows larger than 50MB. Each time the app pool recycles, the application will have to restart which will be a big hindrance on performance for the site. You could try disabling the various caching mechanisms to cut down on the amount of memory the app uses but that will also make the site run slowly.
In short, if your host is placing such a ridiculous limitation on your site, get better hosting.
HTH,
Joe D.