Well, as usual, even though I was not even searching for this specific Hippolyte Bayard process at all, browsing the internet I hit on the work of Tania Passafiume for the George Eastman House back in 2001...
Seems she dug into the direct positive process and Bayard quite deeply. Haven't had the time to really go through this 64 page PDF document, but it sure seems interesting enough:
Reading some comments though, it seems quite clear that the potassium iodide was applied before exposure, see the "What is the chemical reaction?" section on page 7.
Tannia also shows some detailed instructions for re-creating the process.
I think some of you that seem to be following my posts here on APUG are going to love this document!