This would be extremely risky and I do not recommend doing so. One suggestion I have is getting a decent PC from Dell, HP, Asus, etc. that comes with and i7 or can be easily upgraded to an i7 (you could also build your own PC) . You can install OS X on the PC using a tool like UniBeast and an external hardrive. You can use your current mac as a monitor. While this will be much more expensive than just upgrading your CPU, it will be much less risky, and future upgrades such as a GPU upgrade will be much easier (along with many other perks of having a PC case to hold your parts).
Hope this can help!
-Garrett