Two week ago, I had to upgrade a switch stack at a customer location to the newest IOS release. While doing the upgrade, I have seen the command the command is available to disable Stackports, but i have not tried it myself.
I suggest you can try upgrading your switch and then you should be able to disable Stackports as you wish......
Hope this helps
I am sorry. You are right. This was recently added to new IOS released for the 3750 switches.
Please check the link below: