I finally had a chance to try the 'bookmarklet' workaround suggested by Micah that is documented on Liz Castro's blog
Pigs, Gourds, and Wikis. I had to modify the procedure a little to work on my iPod, and it is a little awkward, but it does work.
In particular, the bookmarklet only works with the 'full' Overdrive web site, so I needed to figure out the url to use for my library's 'full' (non mobile) overdrive web site/portal (bookmaking that for future use), so that I could run the bookmarklet in the appropriate context. After doing so, 'Download' executes the new javascript that gives a 'Open in Bluefire' choice.
If I get some time I'll see if the 'bookmarklet' approach can be adopted to work with the mobile Overdrive site, since that is easier to navigate on an iPod/iPhone, and it is the one that the OMC application launches.