The command that’s used to convert a dropped file to markdown can be simply re-worked to "convert from html" command. I’ve attached it, but you can also simply install the attached command.
I’ve simply opened the command Bundles -> Markdown -> File Drop Actions -> Insert HTML File as Markdown.
Copied the contents of the drop action to a new command (Cmd + N, select Command from the dropdown). Be sure that the new command is in the "Markdown" bundle, or the script that does the conversion won’t be located where its expected.
As for #2, I think the short answer is "no". I’ve looked in the included version of the code, and I don’t see the support for this just. That said, there does seem to be a new version that might. Perhaps the file could be upgraded?