Aligning math environments

[Yang]

Can I insert environments like {lgathered} or {gathered}[t] without
resorting to raw TeX? E.g., how would I go about adding the following
into my document?

\begin{align}
 x &=
\begin{lgathered}[t]
    a + b + c \\
    d + e + \begin{gathered}[t]
              f + g + h \\
              i + j + k
            \end{gathered}
  \end{lgathered}
\end{align}

Thanks in advance.