Actually, I’ve discovered a clever way to do what I want, so I thought I’d share it here. Visual Studio allows you to call external tools from within VS. You can use this feature to call MultiEdit, opening the current file you are working in.
Go to Tools -> External Tools… in the Visual Studio menu.
This allows you to open the current file in MultiEdit You’ll go to the exact line and column number. After you save this, you can also click the Move Up button to make it the first command in the list. The tools you add here map into a fixed number of External Command menu placeholders, I think there’s 13 of them.
If you want to save the file first, you can set up a macro to save the file automatically before launching into ME, here’s the VS macro code to do that, assuming you are using the first External Command placeholder to call MultiEdit: