Uncovering a formula line by line (Beamer)

[s nedunuri]

Hello I am trying to uncover a formula line by line. The Beamer User 
Guide suggests the following:

\begin{align}
A &= B \\
\uncover<2->{&= C \\}
\uncover<3->{&= D}
\end{align}
The problem is that when I try to do this in Lyx by "Insert | TeX" as 
soon as I type the "<" symbol Lyx immediately jumps out of TeX mode and 
into the surrounding math environment. Any suggestions?

thanks