populate users in new custom field

populate users in new custom field

Hi,
 
I am trying to add a new custom field that would allow the sales support team member names to be added. However, I would like to add the names from the zoho user list (users I have licenses for). This would allow it to automatically populate from the user table rather than I having to add a pick list and then enter names of team members that would not be automatically updates as people come and go.
I realize that the leadowner/accountowner/potentialowner are all taking this name from the same table. Currently the property show the following location.  https://crm.zoho.com/crm/Create.do?module=Leads&isload=
 
Any suggestions how I can do this?
 
Thanks,
Sumeet