Combing ZIP version with MOBI (or AZW,etc) format of the same book

Is there a way to combine an Audiobook type (ZIP) with an eBook (say MOBI) type into the same book entry? I know this works if you have multiple eBook types of the same book (MOBI, AZW, etc). You end up with one entry in the book list, but the Book Details pains shows "Formats: MOBI, AZW" (or whichever types you have). You can then pick and choose which type to transfer to various devices.

But I can't figure out how to combine the Audio and the eBook entries for the same book. That way I won't have duplicate entries in the book list if I have both versions

Thanks!