I think you can use the the "python" mel command to send a string as python commands.
I'm using it this way:
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menuItem -l "Wiimote Device Editor" -c "python(\"from cra_wiiMan import *\\ncra_wiiMan()\")";
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Escaping each line by \\n as it is also within a string so you have to escape \ to \\ to use the \n (new line) escape code . You need having your py file in one of you scripts directories or PYTHONPATH defined directories to import it properly.
Don't know if that's what you're asking. Hope it helps.