Variables and the mode attribute in apply-templates

I wish to decide between calling one of a set of templates depending on
a fragment of xml (/content/layout/node()).

Rather than having a mass of xsl:when/choose statements, I thought I
would add :

<xsl:apply-templates select="xxx" mode="{/content/layout/node()}"/>

That didn't work. I then tried setting an xsl:variable and doing
mode="$layout" and that didn't work.
Then I tried setting the mode attribute using xsl:attribute and that
didn't work.

Am I missing out on something at the conceptual level - is this to do
with xsl's statelessness?

Regards,

Ben