Yes, you can do this with a constant. The Sandbox always uses the default value of a constant.
Create a boolean constant for instance "SendEmailWithQueue". Set default value to false, then in your own configuration under project settings go to tab constants add "SendEmailWithQueue" constant and change value to true. Make sure you use the correct configuration (if you have multiple).
Now add this constant (use @ sign to call a constant in MF expression) to a split in your MF and Bob's your uncle!