I looked and couldn't find a way round it. I think it's using the time the picture was shot rather than the file creation time, so you might be able to change this with Exiftools (I have a Lightroom plug-in which does this).
An alternative is to try using the various portfolio apps. Minimal Folio is cheap, while xTrafolio and Foliobook are a bit fancier but may be more promising. Minimal and xTrafolio can both pull images from Dropbox (app) as well as from iTunes which is handy if you use more than one computer, have various presentation features, and allow you to rearrange images in any order you want.