Unfortunately due to the way it has been implemented, there is not a way to add fields to that DAC and have them populated on instantiation, and since it's not selected from the DB like a normal DAC, I do not think events would fire for it.
If you would like to access Roles related to the current Users, this should suffice.
PXSelect<UsersInRoles,
Where<UsersInRoles.userName, Equal<Current<AccessInfo.userName>>>>.Select(this /*Or Base if it's a Graph Extension*/);
As there will likely be multiple Roles per user, you will need to loop.
foreach (UsersInRoles role in PXSelect<UsersInRoles, Where<UsersInRoles.userName, Equal<Current<AccessInfo.userName>>>>.Select(this /*Or Base if it's a Graph Extension*/))
{
//Some thing here
}