Can be done Max! Wish I could draw with PAINT. Another thought (I been thinking about this for a while) Is a jack shaft over to the right side and adding a small chain ring (Freewheeling if necessary) Ebikes have had em for years. e bike freewheeling chainring - Google Search
There is always taking it to a local machine shop and have that bit made but would be a good deal of cash.
Tandems vary, so not sure what would work best/cheaper. Can't wait to see what you do. Post pics and buy bonds!