Ability to start trial for account already on a subscription

Situation: customer is already on plan A; I’d like to start a trial for them for plan B.

Currently, the dev centre does not allow starting a trial when the customer has an active subscription. It would be great if I could start the customer on a trial for a higher plan (on their request) to test other features and potentially upgrade. At the moment, I have to manually set flags and follow up on their trial progress and expiry.