Seeding a green manure cover crop into woodchip mulch

Hello everyone! Here is the backstory to my question: I have roughly a 3/4 acre plot fenced in, about 6,000 square feet of which is currently a wood chip mulched vegetable garden. The rest was very low quality soil which had been abused by roundup for 15+ years by the gentleman who owned my farm before me. I let whatever wanted to grow in the non-gardened areas come up (clovers, grasses, crabgrass, all types of things) and once established, covered them with cardboard and a 4-6" layer of woodchips. At this point I have covered probably 3/4 of my non-gardened in areas this way.

Here's my question: I want to establish a ployculture of green manure crops into this mulch in the spring. How should this best be done? By raking the chips back and planting seeds in dirt? I was considering making seedballs a la Fukuoka but was unsure if plants can grow in just woodchips? Can I just broadcast seeds out before a big rain and let them be washed in?

Thanks for any insights you might have,

Chris

The photo is from Sepp Holzers permaculture book, where I got the idea for this from.

With these tools you could seed or transplant into the mulch

http://highcaloriegardening.blogspot.com/2014/09/single-seed-jab-planters-for-planting.html

http://highcaloriegardening.blogspot.com/2014/09/manual-transplanting-tools-part-one-of.html
http://highcaloriegardening.blogspot.com/2014/09/manual-transplanting-tools-part-2-of-2.html

If you have a few inches of mulch, some larger seeds will find their way through if you get them a little under the soil and rake back the mulch - fava beans do great like this, and other large seeds/tubers will find their way.
If the mulch is not thicker than 2", broadcasting some smaller seed on top, like clover, carrots, and brassicas should have reasonable success.
I will also mention that things like currants raspberries, and blackberries love this wood chip mulching and will establish very well when planted.

Seed balls will work, but you might need to make them larger to have enough soil above the wood chips. The seeds germinate in the seed ball soil and roots go down to find the soil under the wood chips. Need consistant moisture to germinate, so the balls allow this. Fukuoka is seeding into straw/clover on top of soil so any size balls will work.

In the picture, he has compost or some soil medium on top of cardboard, which would work if you add compost or top soil on top of wood chips and seed into it.