Hi,
this is unfortunately no possible in 12.7 up to my knowledge
The best workaround will be to reproduce the important keyword of the content of your attachment into the title/problem/solution of your KB docs or been off from the attachments and right all in your KB (where you can bee limited in size and require good discipline from KB teams.
With newer version you can supposedly use sharepoint to store larger document and use the new search engine but never have set this up yet as my previous experience with the FAST engine of previous version was a disaster.
That say for me the Kb is primarily there to support your incident management for fast resolution and I will encourage people to use it for that purpose vs. replacing a document repository as I don't want to read 500 pages prior to eventually get to my solution.
Just my opinion others people may have other opinions
/J
.