Disable plugin availability on all sub-sites except main site.

I know this question has been asked a hundred times, but I never seem to find an answer that works for me.

Some Background:
On my Multisite install I have some advanced redirects to always send users to the main site for registration. I’m using “Sweet Captcha” on the main site registration page to catch spammers. This works pretty good for my purposes.
However, I allow users to create new sites freely and because I haven’t Network Activated Sweet Captcha, It shows up in their list of available plugins to activate on their sub-sites. I would like it hidden. Most advice in most forums says something to the effect of “Just network activate the plugin and now it’s hidden from sub-site admins” Well, that’s true for the plugin menu itself, however most plugins I’ve ever seen actually add menus and options and warnings and bells and whistles. So no, it’s not hidden at all from sub-site admins. For instance, if I do Network Activate Sweet Captcha, all sub-sites now have a big red warning generated by the plugin at the top of the sub-sites dashboard that they need to set-up Sweet Captcha.

I do not want this behavior. I want to be able to activate Sweet Captcha ONLY on the main site, where I send all registrations to.
In fact, there are several plugins that I would like to activate ONLY on the main site. No network activation, no sub-site activation option.

To further complicate matters I’m using WPMUDEV’s “Pro Sites” plugin to sell access to certain plugins. It works as expected, but right now the only option I see that will do what I want seems to be to create a membership level for something crazy ($10million) and set those plugins to that membership level only. Obviously that is not a solution, and looks stupid.

So, how do I make a plugin only “Available” to the network’s main site?
Thanks.