referring to a jar file outside the project

[Mark Petrovic]

I have a project consisting of a parent and a child.  The child needs a jar 
artifact outside its directory space, but within the parent's space.  E.g.

parent
        lib/thejar.jar
        child
                src/main/java
                etc.

I have a working child build, referring to the thejar.jar thusly

compile.with 
artifact('thegroup:thearti:jar:beta').from(file("../lib/thejar.jar")) 
...

but I don't like the ../lib in the path.

I tried things like project("parent")._("lib/thejar.jar") ... but kept getting 
circular dependency errors.

What is the Buildr Way to refer to the thejar.jar that is in a well-known 
location relative to the parent, but not necessarily the child?

Thanks.

--
Mark Petrovic