How to change speed of texture image sequence

I often need to change the rate at which an image texture updates - ie instead of incrementing every frame it increments every 2 or 3 frames.

I thought I’d found a clever way of doing it by animating the offset number in the texture/image panel.
This used to work but doesn’t any more (since 2.65). Apparently those value were never meant to be animated (I thought the mantra was “everything can be animated”) so its been taken out.

Am I missing a really obvious way of doing it?