Is there any reason not to invoke your script as:

./my_script create --folder empty --size 50 --additional "hey how ---a
+re --you 555"
[download]

That's how pretty much any other command handles such arguments and it is what I as a user would expect to do to feed such an argument to an option.

I asked a similar question on another forum

Would you be so good as to provide a link, please?