How can you remove only certain items from a dynamic picklist?

Hi, this is driving me nuts and I'm wondering if someone can help me figure out how to make this work. I'm a newbie to Deluge and Zoho.

I belong to an organization that provides teams of mentors to mentees. I've created an application with the following forms:

Contacts - where the Role can be defined as a Mentor, Mentee or several other fields
Mentorship Teams - where you can associate contacts based on their role on the team
Mentorship Team Meetings - where we track who attended and what happened at a team meeting.

Mentors can belong to more than one team and multiple mentors belong to each team.

Here is my challenge. After much effort I was able to write script on the Team Meetings form so that on user input selecting the team name, it only populated the attendance check box with the members of that group (both mentors and mentees). However, there are also occasions where a mentor not part of a team may attend one meeting to offer specific feedback in their area of expertise. So, I would like to have Mentor Specialist field that is only populated with the mentors who are not already part of this team. Seems like it should be easy enough but I'm finding it very difficult.

To my thinking I should be able to write a script that says pull in all contacts with the role of mentor but where the team name on the contact form does not equal the team name selected on this form. Hell if I can figure out how to do that though. I keep getting shut down on every attempt to do it. I think some of the issue stems from the fact that the Role is a fixed item you define on the contacts page, whereas the team is a bidirectional relationship with the Teams form and new teams are always being added.

Any help or ideas is greatly appreciated!