This can be done by switching to 2D view before using the Share icon to get a link for your current view of the synth.
In Silverlight: http://photosynth.net/view.aspx?cid=6028b58b-69ff-4bf9-961b-719ff53d8619&m=true&i=0:54:1&t=False
In Direct3D: http://photosynth.net/d3d/photosynth.aspx?cid=6028b58b-69ff-4bf9-961b-719ff53d8619&m=true
It's really the &m=true part that denotes 2D mode, but the Silverlight viewer seems to also want an image number and the t flag, although I don't know what it does off the top of my head.
If you're sending the link to a Windows PC user who runs 3D graphics on their computer a lot and has already installed the Photosynth synther, just go to the Direct3D viewer, copy the URL and add &m=true to the end as I did above, but from what you're telling me, most of the people you'll be sending links to will be using the Silverlight viewer.
Again, just load the synth yourself, switch to 2D, and then get a Share link.