Transfer REST Mailbox message from 32U4 to linino

I'm trying to get a REST Mailbox message to a Python script on the linino side.

A short test message gets from my web page to the 32U4, I can read it using Mailbox.readMessage(). That all works fine. The problem I have is transferring it to the linino side.

The real massage will be quite big, in the region of 1k bytes, and 32U4 RAM is running out, so I don't want to read it out into a buffer first. I need a method to get it across with a small RAM foot-print, reading it out byte-by-byte perhaps. Speed is not an issue as the data will be updated, say weekly, from a web page.

A Python readMesssage() method , avoiding the 32U4 completely, would have been ideal, but I understand that isn't available.

Does anyone have any ideas?