I'm not sure which rental company you used that was not willing to ask the Owner to put in a room request for you.
Two of the biggest rental companies require Owners to put in room requests:
From the sample Intermediary Agreement in the DVC Owner's section of David's website:
The DVC Owner agrees to be responsible for:
5. Processing all reserved guests' requests for optional add-ons and for specific room requests with Disney Vacation Club and/or Walt Disney Company ("Disney").
https://dvcrequest.com/dvc-owners/sample-intermediary-agreement
From the sample Intermediary Agreement in the Members Section of the DVC Rental Store website:
6. DVC Member agrees that upon receipt of requests or direction from The
DVC Rental Store, DVC Member shall:
d. Promptly facilitate directives from The DVC Rental Store on behalf
of the Guest including but not limited to, the addition to a
reservation of
Disney Dining Plan purchases (in which event funds
to make the purchase shall be provided from The DVC Rental Store
to the DVC Member), Magical Express reservations, view location
requests, and Guest modifications (such as name corrections).
Guest is permitted to make requests for preferences or changes
such as: adding and registering additional Guests (if the
accommodation occupancy allows for it) or other location
preferences (with each such addition, request or change defined as
a “Directive”), A single Directive can have more than one allowable
request, change or addition.
https://dvcrentalstore.com/wp-content/uploads/DVC_Rental_Store_Intermediary_Agreement.pdf
I know The Timeshare Store (
www.DVCStore.com) does rentals but they don't have a lot of info on their website.
I don't know what other companies are doing rentals these days.
If you pay for a subscription at
TouringPlans.com, I believe you can put in a room request even if you are just renting and are not the Owner. But I've never tried it myself.
https://touringplans.com/walt-disney-world/room-finder