User Database Plugin Suggestion Of Plugin In General

As far as I can tell, this is what I have not found anywhere at all, and I could really really use this functionality.

Here is what I need it to do:

- Each site has it's own user database
- I do not lose control over that site when this occurs (super-admin auto add to database with this)
- Registration is still the core registration
- I can still use WPMU DEVs Blog Template plugin and create sites

I have been searching the net for hours (at least 8 hrs), and I have finally broken down and needed to ask for help on this somewhere.

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Here is my idea on how I can see this working:

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- Modifies the WP registration to submit it's data to database where database depends on blog

- Modifies the multisite network to create a separate database that holds users and account information separate from the network

- Function that helps define which database that is calling based on a variable (probably blog id)
(So, if blog id = 4 then use database 4 [very basic idea of that])

- Function that allows for choice of this being activated per blog (optional really)

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So basically, this is modifying the core of the registration with a variable upon submission
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Now here is why I need this functionality.

I need to be able to have users sign up to multiple blogs, however, having them networked defeats my invite function, and thus breaks the functionality of my product. Because in order to access content on pages, they need to have a membership. Simply cannot have members signing up and clicking subscribe without putting in an invite code (this occurs when someone is a member of the network, hence the need of this plugin)

Now I have purchased WishList Member Multisite installation pack, because it allowed for invite code tied to membership level (through CM invite codes), which is what I really needed. But I am fully prepared to take that back if the Membership plugin here is able to provide that functionality within the next 28 days. But I digress, this is not about that.

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So as a summary to this epitome of OMG, if anyone has a way to make this work the way I need it too, or if the kind devs here would be willing to help me get this done (I haven't the money to hire anyone to make this for me at this time [product needs to launch first before I can pay anyone {and I have powerful companies waiting to take this product to it's next stage of success, but need it to function first}] ), I would be very appreciative.