Ha, yes, Nagel's paper is excellent on that, of course. And I won't say I have the answers to those issues.
But I think even with drugs or even Virtual Reality simulation, it is not possible to consider your perspective / experience / understanding the same as that of another person. This has to do with the fact that we are always already in the world, as Heidegger would say. And I would extend that to always-already-being-in-your-life/world. Knowledge and they way you see things add up, are not made in a void. And this is what scientific experimentation might forget.
Even if everybody reports the same things (even physical information etc), this doesn't mean it is the same. Okay, insert Deleuze here. (But I'll stop, before this becomes a lecture on contemporary philosophy ;) )