Absolutely, but here's the catch. You're designing the compression and decompression program based on the particular file. So the decompression program is really part of the data that's used to reconstruct the program. (For example you could replace a certain 1MB stretch of random data with a short magic word, but the decompressor would have to contain that 1MB so it knows what to insert when it sees the magic word.) That's why the original challenge measured the length of the data plus the decompressor program.