I am interested to know what is the use case of actually sending fee to admin user in each transaction vs just cutting 5% off the send amounts. Admin user can withdraw anytime as anyway he is having complete access to wallet. Note that if you create extra send output for each payment you are increasing the tx size which would result in higher tx fee as well.
Some services like a Bitcoin exchange, mixer or marketplace could use this feature.
If a multisignature address (this might be a usefull feature too) is used, the admin can't access the funds.