To “[provide] influence” by serving on Obama’s cabinet would require first pledging your loyalty to a man who has promised to advance Planned Parenthood’s goals. Any ostensibly pro-life person who accepted a job working for Obama would be pledging loyalty to a man who is either an avowed abettor to murder or a liar (meaning Obama was lying when he said he’d work for Planned Parenthood’s goals). Any “Christian” who accepts a position on Obama’s cabinet, while still claiming to be pro-life, is giving scandal and should be shunned.
If it is understood up front that you are there to give a biblical perspective, then I don’t see it as compromising your princicples. If you have that option then you take it. If not, then don’t.