Reducing USBD short-transfer delays?


I’m driving a Class 2 fax device over a USB<->Parallel converter
cable, which initialises the device with a normal AT command sequence.
With the device knowing nothing about the 64-byte size alignment,
this involves many short transfers. I’m using USBD_SHORT_TRANSFER_OK
so it doesn’t error each time, but it does still mean I’m having to
wait for the USBD timeout (500-750ms?) before they’re passed through.

Assuming I can’t change anything in the device or converter cable, is
there any way I can reduce or eliminate the delays before the short
transfers are completed?

I’m guessing the USB CDC class must handle this by adding/stripping
padding, but I don’t know of a CDC<->Parallel converter to use

Any help would be much appreciated.