It's true that the package vignettes (available from the package landing page and GitHub Pages) still focus on configuring existing panels.
We have written a book about extending iSEE that describes how new panels can be developed (either as standalone R scripts, or in separate packages that import iSEE, see the iSEEu package for example).
In your case, you're describing a type of panel that hasn't been implemented in iSEE, iSEEu, or any other package compatible with iSEE that I'm aware of.
As such, I think you need to consider implementing your own panel from scratch, as you cannot simply configure an existing panel to reach your desired result.
I suggest that you have a look at the iSEE book linked above, and I very much welcome your feedback on it, including questions and requests for clarifications.
If you do have questions after trying to implement a panel yourself, I suggest you make your code available as a GitHub repository (always a good idea anyway, for version control), open an issue on that repository, and tag me using @kevinrue in that issue, so that I can have a look at your code and guide your through the process if you wish. If you have trouble with that last part, you can also contact me by instant messages on the Bioconductor Slack workspace.