Decreasing the outer margin

How can I decrease the outer margin for the pages of my memoir book, without decreasing the inner margin?

I want to alter the settings I already have, given here:

\documentclass[10pt]{memoir}

\setstocksize{9in}{6in}
\settrimmedsize{\stockheight}{\dimexpr 6in-15mm}{*}
\settypeblocksize{510pt}{270pt}{*}

\setlrmargins{*}{*}{4}
\setulmargins{*}{*}{2}
\setmarginnotes{5mm}{45.23mm}{\onelineskip}
\setlength{\footskip}{3.0\baselineskip}
\checkandfixthelayout

\usepackage{lipsum}

\begin{document}
\lipsum[1-5]
\end{document}

-

Modify \textwidth immediately before \checkandfixthelayout. If you add a positive value to \textwidth, yo have to add the corresponding negative value to \foremargin.

\documentclass[10pt]{memoir}

\setstocksize{9in}{6in}
\settrimmedsize{\stockheight}{\dimexpr 6in-15mm}{*}
\settypeblocksize{510pt}{270pt}{*}

\setlrmargins{*}{*}{4}
\setulmargins{*}{*}{2}
\setmarginnotes{5mm}{45.23mm}{\onelineskip}
\setlength{\footskip}{3.0\baselineskip}

@jamaicanworm I guess you could increase the value of \spinemargin by X pt, while at the same time removing X pt from the changes to \textwidth/foremargin. –  lockstep Apr 16 '12 at 15:42
@jamaicanworm Correction: Remove X pt from the changes to \textwidth , but not from the changes to \foremargin. –  lockstep Apr 16 '12 at 15:44