cachedir ignored?

Perhaps I'm missing something obvious here but I'm trying to get yum, 
running as a non-root user with a custom config file, to cache data 
somewhere other than under /var/tmp.

I'm running repoclosure checks on a bunch of different repos and have 
these entries in my yum config files:

cachedir=/home/paul/lib/repoc/cache
persistdir=/home/paul/lib/repoc/lib

However, nothing is stored in either of these directories and instead I 
get directory /var/tmp/yum-paul-<6-random-characters> filling up with a 
few gigabytes of cache data that I'd rather store elsewhere and not fill 
up the /var partition.

How can I get yum to put this data where I want it?

Cheers, Paul.