SystemJs Builder remove part of name -

i have folder structure after transpile typescript this:
-build
--app
----a
----b
----c

where a,b, , c supposed separate modules , bundled independently. far, can bundles work, system.register names have 'build/app/xxx' in front. want rid of 'build/app' part. how do this?

i've tried using baseurl './' './build/app' no avail. thing changes name altering paths pass builder.bundle 'build/app/a/*' 'a/*'. doesn't work since dont have folder called 'a' on outermost level. have tried path property on builder config '*':'build/app/*' throws errors passes files base directory in.

edit: i'm running builder using gulp. gulpfile @ same level build folder.