… without introducing any undemocratic bias:

Introduce contextual ads made exclusively of product/service comparisons made by  democratically-controlled consumer organizations. In Italy for example there is Altroconsumo org with 100s of thousands of members which regularly produces extensive comparative reports.

In practice: for each new report that comes out, a request is made to the companies producing the product/service in the top 30% to sponsor it publishing inside Wikimedia portals.
Such formula could be extended to Wikimedia video, generating huge funds, arguably without any. Proceed are shared among Wikimedia and the consumer org.

(originally written in 2011, and sent to Jimmy Whale, which found it interesting)