Random-looking primary keys in the range 100000..999999

I'm looking for a way to implement pseudorandom primary keys in the range
100000..999999.

The randomization scheme does not need to be cryptographically strong. As
long as it is not easy to figure out in a few minutes it's good enough.

My starting point for this is the following earlier message to this list:

http://www.postgresql.org/message-id/49F96730.4000706@postnewspapers.com.au

The answer given to it here

http://www.postgresql.org/message-id/448163db-cac5-4e99-8c4c-57cbc6f6af78@mm

...is really cool, but I don't see how to modify it for the case where the
domain of the permutation has a cardinality that is not a power of 2, as it
is in my case (cardinality = 900000).

---

(In the crypto world there are "format preserving encryption" techniques
that probably could do what I want to do, but their focus on cryptographic
strength makes learning and implementing them tough going, plus, the
performance will probably be poor, since high workloads are an asset for
such crypto applications. Since cryptographic strength is not something I
need, I'm trying to find non-crypt-grade alternatives.)

Thanks in advance!

kynn