Your code would have to look something like:

# Module Pasted Here
package Something;

# Code

# End Paste

package main;

#use Something;

# Your code
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If you forget to switch back to package main, or you still try and use the module, you're not going to go very far.

I'm thinking that a quick bit of code would allow you to "attach" modules to your program, perhaps in the __DATA__ section, such that they could be extracted and eval'd. This isn't going to do wonders for the speed of your program, though.