Help porting an exiting number (from a Smarty account) to a new Smarty account. Throws an error.

CallumB_2260120  Unfortunately, you can only port between networks and not between sims on the same network.

Is it not possible to start a group, activate another sim as a 'nickname' account and then have both sims effectively together?  https://help.smarty.co.uk/en/articles/3417277-what-is-a-group-plan

(10% discount for each plan - along as they're not on special offer)