I've seen a bunch of information on how to add  new data types to be used in Document Types, but I'm having a hard time finding out if there is a way to add a new Type to the Parameters list of a Macro. 

Basically, I'm trying to 'idiot' proof a membership control. Right now the control is set-up to receive a string that has the membership types and membership groups that the new user should be assigned to. Since this might be different with every install, it needs to be passed in to the control. Yet, having it passed as a string creates the additional potential that they will enter the information in incorrectly. I'm aware that developers could still screw it up when they are editting the template, but it would still be much easier if they could see a multi-select box with all of the available Membership Groups and Membership Types. 

Thanks,
Chad