You could do the second thing using some relatively simple VBScript glue.
There's an example here which makes a different command run depending on whether a file or directory is selected. If you know a bit of VBScript then it should be easy to adapt to do different things with different file extensions. (If you don't then shout and I'll have a look when I get time.)
Some command-line music converters decide whether to encode or decode automatically depending on the type of file passed to them but I can't remember if LAME does (or can).