Following e-birk's solution a step further, yes you can preview raw TeX code instantly inside LyX 2.0.6.
Go to Tools>preferences>Look&Feel>Display and select Display graphics and instant preview "On".
Type Ctrl+M to insert a new formula region.
Type Ctrl+L inside the math formatted region you created in (2) to insert your raw (La)TeX code.
If necessary, you may need to left click on the TeX code object and give it a second to read your raw LaTeX code and update the display. For tables, right-clicking and selecting "wrap by preview" seems to help when they are not displaying.
Finally, click outside the TeX code input to leave its active state. and you should see the TeX graphic beautifully drawn. If not, left click on it again and then click outside it, it should update with the graphic.
There are some instances where pasting raw LaTex can result in the textual "\backslash" being interpreted rather than programmatic "\". Make sure you first write or paste in the ERT without an environment. Then, add the environment in manually once it is correctly registered as a math equation (you can do this in a text editor with your ERT just copied from Lyx). Now paste it back in (with the environments added manually) and it wont be registered as text but instead as math (because when you copied it from Lyx it was encoded as math not a string).
If the Tex code is copied from LaTex source, usually this backslash isn't an issue. It is mainly an issue when copying from a richly formatted text editor as the newline characters and other invisible formatting gets copied along with it.
There are limitations, especially as you integrate Tex code which contains spaces (since in math mode you cant have spaces with Lyx - that I know of). Worst case scenario, at least you can type everything in ERT.