Another option would be to use a tcl bytecode compiler, such as TclPro's Compiler (
http://www.tcl.tk/software/tclpro/compiler.html). Be adviced though, that if your eggdrop can run the code, then anyone intent on reading your code will be able to do so with enough effort.
I roughly recall some technique using the tcl_traceExec variable being set to 2 prior loading an obfuscated or bytecode compiled script, and then monitoring the generated debug output. This would require a tcl-library compiled with TCL_COMPILE_DEBUG being defined, but that wouldn't be a problem for anyone with slight experience compiling their own libraries...
All in all, if you have some very valuable code, consider using NDA's and legal means to ensure your copyright of the code; enlighten your client of your rights as a copyright holder; and your client's entitlements through the license you grant your client.