How about this for a possible variant: Six months doing actual useful work. In my own field, this could consist of clearing some to-do list items for an open source software project.

I'm not familiar with the industry, so please excuse me if this is a silly questions, but dosen't work on open source projects already help you with signalling competence? And if it dosen't, why is this so? Are there cases of autodidacts who marshal up a impressive enough portfolio of such contributions that they can get hired into entry positions (and later advanced based on their achievements there) without a degree?