Is there any way to "pair" a treaty offer with a resource offer?

I'd like to bribe someone into an economic treaty (to make it easier to attack him later thanks to the road, but he doesn't need to know that). He is at -3 to that idea though. I have lots of stuff he would like but when I offer it to him for free it isn't obvious what it does to his point of view - it certainly doesn't seem to change the initial -3 (but maybe it would over time?)