are there any tricks for fixing or a broken beurre blanc. what about holding?

I've heard you can put it in a blender and just blend it to bring it back together right before you use it.

There is a way to temporarily fix a broken beurre blanc. Just take a small amount of heavy cream and reduce it over low-moderate heat. Once its thick you can re-emulsify the broken beurre blanc by slowly whisking it back into the reduced cream. Don't let the sauce get too hot or it will break again. I like to move the pan back and forth off the heat source to regulate the temperature of the sauce. I generally like to hold the sauce in a container placed in a water bath over the stove. That way the sauce is kept over gentle heat.

Not sure what you mean, but maybe try whisking a small amount of flour into it, over very gentle heat. :)