Wasn't thinking that,
another option you could try without voiding psu Warr.
look at creating a 'shelf' for the new psu from the mobo back panel/tray cut out a
*Cant draw it lol, imagine a small n shape, elongate the horizontal bar.
shaped line in your backpanel, fold it down towards the inside of the case for the psu to sit on, obv make sure it comes far enough into the case to provide decent support for the psu, a 1/4 inch wont do it
my original idea was to remove the psu's case ( voiding your warranty)
place it to where it would be installed and drill 4 holes in the roof panel, fix bolts through pinning the case to the roof then put the gubbins part of psu in and re-close that up,
fair bit of work either way tbh, but if you dont want to grease your warranty, I'd recommend the folding tab/shelf option
Moto