Have you just tried it to see what it does? Once you've created the equip profile for your 2.5 gal batch it's a snap to scale your recipe. I haven't tried it, but presumably if you provide your losses, those will factor into scaling. Give it a try and post back.
Goat Mountain Brewery (GMB)
A 10 Gal all-eletric nanobrewery nestled in the foothills of the cascades. My own slice of paradise.