Ok I was doing a bit of searching around the iGEM site and I found
this part (which is in the kit) BBa_J61035. I can't explain it as
well as going to look at it yourselves, but basically it involves an
insertion of the gentamycin resistance gene into the biobrick prefix
ahead of the RBS such that you can select for the incorporation of the
RBS ahead of something and then tack your promoter on the front in the
next step.
Have a look and see what you think