I know that you have said that this is under the MIT license with the Gentleman's agreement of not distributing this as a standalone product, but I think you are taking the wrong approach by stating it like that. The MIT license has an expectation with those that know about it as being essentially do what you want to it.
A better approach since you want to modify the license is to use one that allows that sort of thing by design.
I would recommend using a license like the No License, which restricts most things, but allows you to specifically unrestrict them at your digression. It is essentially a "Build your own" license.
The No license looks like this by default.
Copyright [year] [fullname]
And you just add the specific things you unrestrict after it.
These are the default rules to No License.
How to apply this license
Simply do nothing, though including a copyright notice is recommended.
Note: This option may be subject to the Terms Of Use of the site where you publish your source code.
Required
I know that you have said that this is under the MIT license with the Gentleman's agreement of not distributing this as a standalone product, but I think you are taking the wrong approach by stating it like that. The MIT license has an expectation with those that know about it as being essentially do what you want to it.
A better approach since you want to modify the license is to use one that allows that sort of thing by design.
Here is a site that gives and easy to use breakdown of different open source licenses. http://choosealicense.com/licenses/
I would recommend using a license like the No License, which restricts most things, but allows you to specifically unrestrict them at your digression. It is essentially a "Build your own" license.
The No license looks like this by default.
Copyright [year] [fullname]
And you just add the specific things you unrestrict after it.
These are the default rules to No License.
How to apply this license
Simply do nothing, though including a copyright notice is recommended.
Note: This option may be subject to the Terms Of Use of the site where you publish your source code. Required
License and copyright notice Permitted
Commercial Use Private Use Forbidden
Distribution Modification Sublicensing