Well, Vader got VERY close the Leia and didn't notice the link (like I say, a DNA profile would have been trouble...). If anything, that only reinforces my point.
If he had thought there was a Force adept on that ship, he would have reacted VERY differently.
And what else do people think that Vader would say about someone who is giving him toruble? He wouldn't blame his skill anmd he doesn't beleive in luck. So- "The Force is Strong with this one". Incredibly reasonable.
AND no-one has yet done anthing about the bad logic of the situation. Luke was not using the Force at the time. He wasn't doing anything that a normal person could not have done. Until he bullseyed the port, he didn't do anything abnormal. We have no reason to suspect that Vader could sense anything from him, passive or otherwise.
Why overcomplicate? NEVER overcomplicate. My explanation stands the eaiest.