Take all the bishoprics, cities, everything. Then, when literally every single Irish holding is in your control (NOT before, if before everything, some vassals will still hate you) right click on the minor holdings in each country, and click on the lower-left part of the triangle to create a character to control that holding. Since he will be a clean slate, he won't have the tyranny penalty on you.
That should clean up your vassals. Then, give out a bunch of the counties to either cities or bishops in those counties (click on the shield on the minor holding, then click on the character portrait on the bottom of the screen, then click on the diplomacy button, and grant them the county they reside in)
If you want, you can give out the duchies too.
The end result? Your court hates you, but every single vassal will either like or dislike you. It's a clean slate. They have no tyranny penalty, just the normal pluses and minuses in vassal relationships, with a possible starting boost to the counts since you gave them land (they might desire the duchy, though, which will give them a malus. You can give the duchy to a count, it'll make them more powerful, yes, but you only have to control 10 or so dukes instead of 40 counts)
That will take a lot of clicking, but it's worth it. I've done it a few times, once or twice.