I'd advise you not to CrossFire the card at all. The 4250 is an extremely low-end card, and is not worth it to add another one to CrossFire. Your best bet is to get a higher-end card (for example, a 5650 will be a huge improvement at a low cost).
P.S: You can't CrossFire it with any card, since it's an integrated GPU, so your only option is to buy a new GPU.
Hybrid Crossfire only worked with the lower end 3xxx series cards, more modern cards dont support it because they are all orders of magnitude more powerful than the IGP so it wouldnt give any notable benefit, so while its still listed as a selling point its not really usable these days.
Even a low end card like a 5570 would provide much better performance than a 3470 in hybrid crossfire with your IGP.