Bulk delete of iMessage attachments from iCloud (not from device)

I have iMessages backed up using iCloud.

Unfortunately the attachments quickly chew up the 5GB of free space.

I'm not interested in buying more space as this just kicks the problem of storage down the road instead of solving it.

What I want is the ability to access iCloud itself (not the storage on my devices) and then selectively purge iMessage attachments. I want to do this message thread by message thread, but I also want to be able to do a bulk delete of ALL attachments too.

From what I can see, these options don't exist.

If they do, can someone show me how to use them? If they don't, is there a way to encourage Apple to make it available?