Yes, this is entirely possible. Though you will need a monitor with multiple inputs, or two monitors. The problem resides in telling which card to do what, ie task differentiating. The programs used may allow for choosing the card to be utilized. Or using the bios or control panel to enable/ disable preferred card. Though having an extra card may not be necessary, programs such as solid edge, autocad, keyshot are designed to use the cpu for heavy rendering, limiting the need of a a commercial gpu. In other words, your 7970 should be more than sufficient for the task of cad work.I run all three of these programs exceptionally well on one of my 7870s without even making it sweat.
Asus Sabertooth 990fx r2.0, AMD 8350fx @ 4.8Ghz w/ Corsair H80i, Dual Sapphire 7870 ghz edition OC, 24GB G. Skill 12800CL 9-9-9-24 @1600Mhz, 120GB Kingston SSDNow!, 1TB SG MomentusXT SSHD, Corsair TX850M, Matshita Blu-Ray Burner, Logitech G930 7.1 Headset, Razer Deathstalker Keyboard, Razer Mamba Wireless Mouse, Tri-Asus vg23a 3D Monitors