F12 to open the console.
First enter the following command:
var r = cr_getC2Runtime();
Then, enter the first level, and enter this:
r.all_global_vars[7].data=5
Exit back to the menu with the hamburger button in the top-right, and enter your newly-unlocked level 5.
Repeat this process two more times, but changing the final number in the command to "10" and "15" respectively, and entering those levels once they are unlocked.
Cheese contributed by GENiEBEN 
