Why not propose changes to the way the UN works? Have all the members (or at least the Security Council -permanent and temporary) figure out what the US proposes. After all, there are always changes at the UN, like new members coming in (Switserland) and conflicts arising, others dwindling and new nations being created (East-Timor).
The UN is not a completely static institution and it has no coercive power, only coordination power.
Now, if some unlikely country (with a dictator at its helm) gets a human right commission (temprary), the idea is to have several countries of each continent being part of the commission.
Think a little: if a country accepts to be part of the commission, it will be much harder for it not to accept scrutiny concerning its human rights record. The UN hasn't just pointed fingers to dictatorships but also democracies where rights of imprisoned people are not respected.
Then again, it can't force a country to behave differently, but it can denounce what's going on.

Raoul