Luckily some posts have inspired me to a solution: Calculate for every standard class level feature (save boni, attack bonus, caster level, bonus feats, special abilities, ...) the hero point equivalent, then give out only 8 hero points per level. Then the players can buy a normal level, a whole hero level or something between. This generic approach, which kills the distinction between classes, can be restricted, by some features for a class must be selected (a wizard has to get a higher caster level, for example). If this approach should not function for every standard class then it could be because they are not rightly balanced. This should be no issue with the revised edition. This method seems also to be great way to balance out prestige classes.