A simple remix of the gridfinity divider bin that allows you to pause the print and place the glass slide mid print, the printer will print over the top of it; holding it in place. 

Pause the print at the layer that bridging starts, place the window in the slot and the printed spacer on top of the window. Ensure the spacer is below the last printed layer before resuming. 

Tolerances are quite important with this print, if things don't line up correctly, you're gonna end up having nozzle crashes, it's quite easy to see if this is going to happen before you resume the print, so just make sure you double check. The spacer has thin walls that may be difficult to print, however I managed it with an 0.6mm nozzle with the newest version of prusaslicer.

I've updated the files after some tweaking, things look a bit nicer and it's far easier to get the glass in place without messing up the next layer. I've also noticed that high speeds and high cooling can both result in the spacer getting lifted up and potentially ruining the print; I used a modifier in prusaslicer to decrease the speed over the top of the spacer to 30mm/s and this has given much more consistent results.