Custom file extensions for XML formatted files in IIS

Hi!

Situation:

1. We use files with custom extensions, lets say .abcd
2. For this abcd type of files we have custom program, lets say abcdmanager - file type is assosiated with the program abcdmanager in Windows, so clicking on file X.abcd abcdmanager opens it in Windows explorer
3. Actually those .abcd files are xml files
4. We use IE 8-10 and IIS 7-8 in our environment
5. If I try to open -abcd file from IIS site I'll get error 404.3 - because MIME type for abcd type of files is not registered

Questions:

1. Is it somehow possible on IE side to declare that abcd files should be automatcally opened with abcdmanager from IIS site?
2. If I declare .abcd MIME type in IIS as application/octet-stream, IE browser will open it as XML file in browser (probably because the content of abcd file is in xml format) - what to do to assosiate abcd file with our customa application abcdmanager in IIS?

Thanks!,

UV