Actually, Pathfinder has gone the route that the existing knowledges are more broadly applicable. So for instance knowledge: engineer will actually let you design various engineering related things as far as how various things have noted its use, it's why I note "you can probably just use knowledge: religion to cover knowledge: philosophy". Yes, in the case of things you come up with via engineering, you would need relevant crafts to then actually create them beyond the level of a blueprint or the equivalent, but that's more the whole architect/construction worker split.
Otherwise you can just take a related profession skill to cover something that would otherwise make no sense for your character to take a different base skills for, like if you don't particularly want the broad knowledge, or it's some skill that just has nothing to do with your shtick. So let's say there was some hypothetical gambler who did what they did via card counting and knowing percentages and the like instead of cold reading and manipulating people. The first guy would use something like Profession: Gambler or something, the second guy would use Bluff. And the actual skill rating would determine who was better.