The granting employees the $5 tip a week idea is pretty good. There are a lot of businesses out there that see the value of open source but don't currently fund development. There are certainly companies out there where the reason for not funding is more logistical than financial. Giving employees the ability to send money to where they see it can do the most good would be a great way to target worthy projects.

With sufficient freedom, I can see groups of employees organise themselves to coordinate development of features that are specifically important to their work.