Hi Per,
Thanks for choosing job-dsl!  Your use case sounds (generally) quite familiar.  There are others out there (including my company in the past) who, when they do something like create a new SVN branch, or fork a github repo, want to copy their Jenkins Job Suite too so they can still have all the Jenkins benefits even when they are not working on the trunk / mainline.
Regarding your specific use case, I guess you're using this 
promoted builds plugin and this 
job copy plugin.  Unfortunately, at the moment, neither is supported by the DSL out of the box.  This leaves you with three options:
1. Use the 
configure block support (which lets you effectively code XML directly but with nice Groovy syntax) - this is quite simple to use
2. 
Implement support for these plugins yourself (and submit them to the project for inclusion in the DSL if you like) - again this is quite simple, but a little more work
3. Change the way you are creating your builds - see below
Options 1 and 2 have links in them to get you started.  Option 3 might however be the way to go.  Assuming I'm right in my statement in the opening paragraph about your general usage, may I ask a little about the specifics of your situation?
Question 1: it seems like the significant part of your problem is the copying of elements (beyond the config.xml) from one job's workspace to another. Is this correct?
Question 2: do you have scripts which do the workspace copying at the moment?  If so, you could re-use these and call them from steps created by the Job-DSL. We also do have support for the copyArtifacts plugin hwich might help you
Question 3: Do you use build slaves? Do you build on different Operating Systems?  I know this can make some things difficult
Question 4: do you need to copy the contents of the workspace? Job-Copy doesn't seem to do this, and job-dsl seems to be a very similar solution to what it does do.  Build-Promotion however does access the files of other jobs (i believe) but doesn't move them (I think).  Could you elaborate on this a little for me so I can provide a bit more help as I am guessing this is the nu b of your problem
I hope all these answers and questions make sense. 
Looking forward to hearing from you.