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 right click on the TeX code object and select "Wrap by Preview" and give it a second to read your raw LaTeX code.
Finally, click outside the TeX code input to leave its active state. and you should see the TeX graphic beautifully drawn.
Step 2 is only necessary if you want the pdf to be generated. That is, it will still display in Lyx without being inside a math formatted region.
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 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).