please find attached a small patch that add the gen_image()
functionality to the export-workflow UI.

Thanks for the contribution. I committed a modified version of it:

https://bitbucket.org/galaxy/galaxy-central/commits/0e064a23864c846483b35f893cf0a769dedf24f1

Specifically, I (a) used gen_image directly rather than a wrapper method and (b) added the code to workflow's export template rather than the base template.

I was not able to figure out how to add a patch to the trello card. But
at least i created one ;).

This isn't possible as best I know. Pull requests are the (highly) preferred way to contribute code to the project.

Best,
J.