We have investigated this issue and determined that we must reject this request.
'Thank you for contacting Microsoft regarding your recent PowerPoint design change Request about being able to add Forms without turning on the organization to the Office Store. Support has already raised a design change request to the Product group, asking for the Forms feature in PPT to work despite Let users access the Office store being switched off it was rejected with the following justification: If the option 'Let users access the Office store' is switched off it is by design to get the 'Office 365 has been configured to prevent individual acquisition and execution of Office Store Add-ins' notification and not be able to use the Forms feature in PPT (Please see the Note in the 'Insert an existing form or quiz' section here: This is the feedback I've had from by ticket, it's not good news I'm afraid :(
