Mailto and XSLT

I am posting data as an email attachment with the mime type of .ATT.  I
would like to be able to automatically assign an XSLT to the document and
have it open in IE when the email attachment is opened.  I cannot figure out
how to pass the information with the data so that IE knows to open the file
with the specific XSLT.  Any ideas would be greatly appreciated.  I have
read that it is not a good idea to place processing instructions in the
instance data so I am at a loss to understand how I might be able to get
this to work.