moderncv and cvitem

You can add \hfill followed by \newline to put an empty line, so your entry will look like:

\cvitem{Something looooong}{\hfill \newline Second entry}

You can redefine \cvitem to use a b{...} column instead of the defualt p{...}:

\documentclass{moderncv}
\moderncvstyle{casual}
\moderncvcolor{blue} 
\usepackage{array}

\firstname{John}
\familyname{Doe}

\renewcommand*{\cvitem}[3][.25em]{%
  \begin{tabular}{@{}b{\hintscolumnwidth}@{\hspace{\separatorcolumnwidth}}b{\maincolumnwidth}@{}}%
      \raggedleft\hintstyle{#2} &{#3}%
  \end{tabular}%
  \par\addvspace{#1}}

\begin{document}

\makecvtitle
\cvitem{Something looooong}{Second entry}

\end{document}