I did make some progress on this front doing exactly what I said above. I don't know shadow very well and ended up putting an ^:extern on portal.client.web/submit and then just accessing it as a global. Not completely working yet, but not blocked either.

The portal.client.web namespace isn't doing much that's very interesting. If getting the code built / loaded becomes a headache, I would vendor the bits you need into your app since its mostly just hitting the /submit endpoint on the portal server with edn, json or transit.