Hi Brian,
AFAIK, there is no way of creating the templates entirely on the fly. However, using
LoadTemplate you can load a template from disk and assign it to your ItemTemplate and AlternatingItemTemplate templates.
Right before you load the template, you can build up your ItemTemplate string, write it to disk and then read it again using LoadTemplate. A bit dirty, but it may be a good work around in certain scenarios.
Cheers,
Imar