PetrusOctavianus: Just act like an Avatar of Virtue (it may take some serious role playing), and your Compassion will increase naturally.
mourfin: I like this method best as well.
Some issues with this:
* You have to roleplay the developer's idea of what is virtuous and what is not. For example, while one might consider pacifism to be virtuous, that won't work in this game, as you can't reach partial avatarhood in Valor without doing so. (The only nonviolent way, to my knowledge, to boost Valor is to throw the skull into the abyss, and I believe that can only be done once per games, and that one time isn't enough.)
* In some cases, the method that works best is not the one that fits roleplaying; donating money is a good example. Donating 9999 gold is no better for compassion than donating only 1 at a time. Also, talking to the same person repeatedly to raise your virtue, while possible in some situations (and good for some virtues), seems rather silly from a roleplaying perspective. (Hast thou always been just? No. (Honestly increased.) *talks to the flame again* Hast thou always been just? No. (More Honesty increased.) *repeat until maxed*)
* It seems silly that you can redeem yourself so cheaply. Cheat the reagent seller to get a ton of reagents, then, for less than the cost of reagents, you can redeem yourself to get all your virtue back. (In computer versions, this will happen easily by buying the reagents normally; the NES version has a cooldown on virtue gains this way, but the cost of cheating the reagent seller isn't as big a deal; I think it's worth it to get 99 Mandrake Roots for 1 gold instead of 1980.) Ultima 5 also has an issue with this; steal from Lord British, then donate a tiny portion of it to get your Karma back. (Or, of course, in U5 you can get your Karma back to 75 at the cost of potentially all your XP by dropping your companions off in the bar and then deathwarping.)
As I said, Ultima 4 can't be played pacifist, even though that would seem to fit the idea of being virtuous. On the other hand, Ultima 6 can be; the speedrun is pretty close to a pacifist run (except, of course, for the part where the Avatar kills an innocent person and takes the rune they're carrying). Also, in Ultime 6, why is killing (and then looting the dead body) not as bad as stealing via spell (and leaving the person alive)?
Incidentally, one thing I am wondering about Ultima 4 virtue wise: If the guards are after you and they attack, is it bettre (for virtue) to fight or run away? (Of course, in U4, getting into a fight with the guards won't happen if you are playing virtuously; Ultima 5, on the other hand, is another matter.)