Replacement for Varien_data_collection

You don't.

But there are 3 ways you can if you wanted to, they can all be circumvented because of open source, thankfully.

Parse source or something
Crawl the web and parse the source or an url for a custom comment/id/whatever.
Chance of failure: Really High - unless you're Google

Create an API
Call home with an API
Chance of failure: High - you have better things to do

Custom Response Header
Create a custom response header
Chance of failure: Medium - this is the only realistic way you can crawl the web and it's easy to implement (and disable) , it's also annoying unless so you better have a good reason.

Case in point ..

.... don't pollute the internet with custom headers...

You're suggestion to hide it via CSS would incur the wrath of satan himself. Seriously though don't do that, ever.

ps . There is a 4th option but I'm certainly not telling you since your motives are unclear.