Extra commands when starting X

[Jan Willem Stumpel <jstumpel@planet.nl>]

I am experimenting with the new input methods like uim, anthy,
scim. Some sites tell me to do things like

  Please add the following line to the ~/.xsession or ~/.xinitrc.
    export XMODIFIERS=@im=uim-anthy
    exec uim-xim&

But in Debian, neither ~/.xsession nor ~/.xinitrc exist by
default. And if you create them, you cannot use them for *adding*
things to the X start-up process. If you do, X refuses to start.
They can only be used to specify the *whole* X start-up process.
For instance, calling the window manager should be the last line.

This may be a frosty FAQ, but I could not find the answer in spite
of much Googling. What is the "Debian way" to execute some "extra"
commands (on a per-user basis) each time X is started? It seems
Mandrake has a ~/.i18n file for this purpose. Is the only answer
in Debian to put something (system-wide) in /etc/X11/Xsession.d?

Regards, Jan