So here's what I did. I'm sure this is not the best solution but it works. MSSQL only.
In my features SchemaUpgradeScripts folder, I added this create for the stored proc below in a config file:
CREATE PROCEDURE [dbo].[proc_roles_insert_at_setup]
AS
BEGIN
DECLARE @RoleGuid uniqueidentifier
, @SiteGuid uniqueidentifier
, @SiteID int
, @RoleName nvarchar(50)
SELECT TOP 1 @SiteGuid = SiteGuid
FROM mp_Sites
WHERE SiteID = 1
SELECT @SiteID = 1
,@RoleName = 'BizzDok Admin'
,@RoleGuid = NEWID()
execute [dbo].[mp_Roles_Insert] @RoleGuid, @SiteGuid, @SiteID, @RoleName
SELECT @RoleName = 'BizzDok User'
,@RoleGuid = NEWID()
execute [dbo].[mp_Roles_Insert] @RoleGuid, @SiteGuid, @SiteID, @RoleName
END
GO
Then I execute that proc along with other custom SQL in another config file
EXECUTE proc_roles_insert_at_setup
GO
The stored proc [dbo].[mp_Roles_Insert] is a standard stored proc in mojoPortal
That gets me the 2 new Roles I wanted when mojoPortal installs.