spoof history.length - browser.sessionhistory.max_entries

ip-check.info demonstrated, history.length can be read.

They recommend:

The number of visited pages should be reset to 2 whenever you change to a new domain.

Open about:config and set browser.sessionhistory.max_entries to 2.

What about doing this with TorButton?

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information