The problem with doing that is, instead of sharing the load, like it normally does, it just causes max load on both chips, so instead of one running at 80° (which is what it runs at with only one chip working), both run at 87 ° ( which is too high for extended periods of play ) , when they both should be running at max 71°. The advantage of the 690 was that the chips always shared load, that solution will only cause massive problems over time.
In short, it is not a viable solution. With skyrim, fo3, fo nv, oblivion AND eso there is a multi gpu option, or a custom option that has multi gpu enabled, in this game there is neither. There is single, and then that force alternate framerate nonsense.