Using free trial period for all levels

Hi there,

ProSites offers a to enable free trial period, which is exactly what I want my customers to have. But I would like this option for all customers and therefore for all different ProSites levels I offer. I would further like them to have all the features of the best account offered within that period and be downgraded after the trial to the subscription they assigned to.
When setting up the free trial, I can always only specify one level users are assigned to. I expected this to apply to all new users. Unfortunately, it always only works within the defined level.
Is there any possibility to set the free trial for all levels and with the highest level features?

There is the option of using coupons for the first month and setting them for all levels, but users would have to enter the code themselves, and that is definitely nothing they should have to do to get a free trial.

Thanks in advance,
Anna