Making standalone builds without encryption would violate media agreements between the artist selling media.
As encryption is the only thing that protects our media when a game is published. Bad enough we can not encrypt everything, scripts, music, it all.
I would build each level as a separate build and then link them with your external program that way.
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit, Screen resolution 1680 x 1050.