So I have set up a few companies (a Coop, a non-profit and C-Corp, LTD, B.V.) in the Netherlands just for this purpose. You register yourself as a cofounder/owner of this company (free) and put $4500 in the company bank account. You now qualify for a working visa and can start roaming all over the EU.
I'm a little vague here, because I want to sell you all the advice and legal work to set all this up for $1000. You first get advice from all the other Americans I helped emigrate to Europe over the years. morphle at ziggo dot nl
Without my help it will cost you a few months, three visits to the Netherlands, setting up a company from scratch and hiring a notary, a lawyer and an expat fiscal tax lawyer for at least $19.000 all together.