Community Builder Custom Plugin

We are in need of a custom plugin for community builder 1.2. This plugin should attach itself to the registration function. (i.e. registration page similar to how cb captcha does.) This plugin should check for a member id and check digit upon registration from a mysql table(ajax style please..:-p). If the combination exists in the mysql table it should allow them to complete the registration and set them into the group associated with that combination(a third field is associated in Community Builder for the member levels). We've tried several other ways, however, to no avail. The plugin should be able to also set the combination as 'taken' and not allow registration of that member ID and csv combo again.