I'm not the most proficient in using it myself but have a copy of the virgin mobile APN's (apns.xml) saved. Extract the framework-res.apk from the ROM and using the 7zip program (or similar program of your choice) select the the framework app and navigate to the folder res/xml/apns.xml. Replace the apns.xml with the copy of the virgin mobile one. Then an easy way to get them into the rom is to rezip the ROM files with your now modified framework-res.apk and flash as new.
I believe some people have posted ways to do this using adb commands but I like to avoid using that if possible.
When the ROM installs if it worked properly then the VM info should appear when you go into the messaging app/settings/mms.
My guess is since this is a port from a GSM created ROM, simply replacing the APN's will not be enough to get the MMS fully functional, other changes may need to be made to the build.prop or jar but at least is a place to start and go from there.