Sadly, there is no visual control like this yet. I have previously wished that Microsoft would integrate their Pivot technology into Photosynth's 2D view (since they use the same underlying image formats), but there has been nothing to suggest that that will happen anytime soon.
About Pivot: http://www.microsoft.com/silverlight/pivotviewer/
On a much more primitive level, if you wish to simply traverse the photos in a synth in a chronological or reverse-chronological order, you can use the fullstop [.] or comma [,] keys, respectively. Unfortunately, this is based, not on the date metadata in the photos' EXIF fields, but on the alphanumeric order of the photos' filenames.
A full list of shortcut keys can be found at the end of the Photosynth Photography Guide: http://photosynth.net/help.aspx#photosynthhelp