Just tried something that worked amazingly good.
1) Connect your PSP
2) Open ComicRack, open an eComic, do File->Save eComic as... and select "Folder with jpeg images" as type
3) Browse in the save dialog to your PSP Photo Folder (in my case G:\PSP\PHOTO) and hit save.
4) Disconnect your PSP, go to photo and select the new comic folder :)
Reading on the PSP works amazingly well. Maybe it would be a good idea to add a 480 width conversion to the save function, so that the comics are already properly scaled. It would also be cool if the PSP could retain the current zoom state when changing pictures.