first, the homeowner did not tie into the power line, the power company did. Unless there is a meter at the road or whatever place the underground power starts, the power lines are under the control of the power company.
Now, the problem is you cannot make connections without a junction box which with the power company is typically a small pedastal box. Depending exactly what is in the easement grant and how large the easement is, this could be an encroachment not legally allowed within the easement (although it could simply be removed to off the side of the easement).
Next thing is you may be able to sue the neighbor under an unjust enrichment claim. You're right, it isn;t fair he benefits from your installation without sharing in the costs. I haven't done any research to prove this is even remotely possible but the courts are often deciding in the name of fairness and equity. It's a cheap lawsuit to file so really what do you have to lose?