For one, I list open-source projects that I contribute to and plan on using and enhancing as part of whatever business objectives I'm being hired to work towards.

Also, I add in a clause that states I will more than likely release aspects of the project under an open-source license. Nothing binding, but I like to have it in writing on the same piece of paper that ensures I get paid for whatever I do. Their lawyers always find a way to bill a few hours worth of figuring out the language. :)

The only thing I ever get from people is something along the lines of "hmm, we don't normally get this request, but no one seems to have a problem with it."

Development teams and managers love it because it means you're writing nice, modular code.

I've never had anyone take issue when, instead of burying some specific bit of functionality within business logic, abstracting things out to a library. In fact, most people would agree that that is good habit to have. ;)

When it is finished you just talk to someone up the chain about releasing it. Normally saying something along the lines of "hey, we might get people who don't work for this company enhancing this feature for us" really helps to sway their decision in your (and my hippie-dippie share things for the greater good) favor.

Here's the language from a recent contract:

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4 . Ownership.

A. Assignment. Consultant agrees that all copyrightable material, notes, records, drawings, designs, inventions, improvements, developments, discoveries and trade secrets
conceived, discovered, developed or reduced to practice by Consultant, solely or in collaboration with others, during the term of this Agreement and arising out of or in connection with performing the Services under this Agreement (collectively, “Inventions”), are the sole property of the
Company except that Consultant may contribute certain modifications to Open Source projects as set forth in Sections 4.A.1 through 4.A.3. Consultant also agrees to assign (or cause to be assigned) and hereby irrevocably assigns fully to the Company all Inventions and any copyrights, patents, mask work rights or other intellectual property rights relating to all Inventions.

( 1 ) Open Source Projects. A software project is said to be an Open Source project when its project materials such as source code are published publicly and its software license permits the combination of project materials with other software project materials without fee and commonly with no or limited exclusivity or other limits on use.

( 2 ) Combined Projects. Consultant may from time to time in the course of performing Services and subject to approval by the Company use Open Source projects exclusively licensed under the MIT License to develop Inventions. During and after the use of Open Source projects, Consultant may add, change, improve or otherwise make modifications to Open Source
project source code or other materials and may contribute these and only these modifications to the Open Source projects provided that these modifications do not contain Confidential Information and subject to the terms of the applicable Open Source project license and the project’s administrative rules.

( 3 ) Notification of use. Consultant has attached hereto a list of Open Source projects that Consultant may use to create Inventions and to which Consultant would like to contribute back non-confidential modifications. Consultant will provide prior written notice to the Company prior to using any additional Open Source projects to which Consultant would like to contribute back non-confidential modifications; and such use shall be subject to approval by the Company.