I think it is relatively complicated.
First you would need to set a property on the new ticket through advanced assignment so:

Set: workitem_has_attachments
To: WORKITEM(workitem_has_attachments)

Then you would need to run the Stored Procedure dbo.sp_addattachment which require the following parameters:
@worker_id, @workitem_number, @workitem_version, @set_clause

So possibly a relatively complicated HDQUERY might be able to exec this stroed procedure with the right values?

John Golembiewski
Midwest Practice Principal
ITS Partners
Jgo@itsdelivers

Yes I know that whe need an HDQUERY. I just don't know how to write it.

I might make an alternate suggestion to you.
Link the incident and make sure people know to check for attachments on the "Parent" incident. I'd be concerned you'd run out of disk space copying the attachments.
Not what you asked, but I'd still think it a viable solution.

No need to worry about disk space each ticket would point back to the same file so there would only be one on file that they all point to.