I suspect you already have one. In dealing with others, I think most people use interpersonal utility comparisons all the time as a factor in their own decision making.
So, to be clear, I think you have one as well, and are really just waiting for those who have another interpersonal utility weighting, which they claim is "true", to rationally support their supposed truth. I've been waiting for that one. Harassed a number of people over at Sam Harris's web site asking about it.
It sounds like we are mostly in agreement, but there is an important difference between me getting utility from other people getting utility (for instance, I would prefer to occupy a world where my friend is having a pleasant experience to one in which he is not, all else equal) and me performing arithmetic using values from different people's utility functions and obtaining a result that would be unobjectionable like the result of adding or subtracting apples would be. In other words, me engaging in a kind of "interpersonal utility comparison" is only really telling us about my preferences, not about a uniquely correct calculation of "utility-stuff" that tells us about everyone's (combined) preferences.
I don't think non-cognitivism is the whole story on morality. People make moral distinctions, and some part of that is cognitively mediated, even when not verbally mediated. One cognitively recognizes a pattern one has a non-cognitive response to.
Nor do I, which is why I am still considering other hypothesis (for instance, virtue ethics, egoism, and contractarianism, all of which seem much more likely to be true than utilitarianism).
Many people on Less Wrong believe reducing existential risk is one of the most important causes. Most arguments to this effect point out the horrible consequences: everyone now living would die (or face something even worse). The situation becomes even worse if we also consider future generations. Such an argument, as spelt out in Nick Bostrom's latest paper on the topic, for instance, should strike many consequentialists as persuading. But of course, not everyone's a consequentialist, and on other approaches it's far from obvious that existential risk should come out on top. Might it be worth to spend some more time investigating arguments for existential risk reduction that don't presuppose consequentialism? Of course, "non-consequentialism" is a very diverse category, and I'd be surprised if there were a single argument that covered all its members.