In Poland, for example, the chairman of this regulatory body has 4 year term and is unremovable. So he doesn't have many reasons to be political.
He has to be political to get the position in the first place and then again if he wants to get renewed (assuming it's not limited) or if he wants to move to a higher position after the four year. The only way to make it minimally political is to have the term limited to one and have the person be ineligible for any political appointment or government job of any kind at the end of the term.