Wanting to auto-select & hide payment methods

I've got a couple of instances in my site where the user would wind up with only one payment method at the checkout.

In these instances I'd like to have the payment method hidden completely so that there's as few clicks as possible.

I've successfully run a counter to only display payment methods when the count of the foreach loop is greater than one. But I've run into an issue with the way that OC seems to sometimes default-select the payment option, sometimes not.

I've wound up with test scenarios where the payment method is (correctly) hidden, but get warning that I must select a payment method - meaning that there IS a single payment method, but it's sitting there hidden and unselected.

Has anyone tried to achieve something like this previously?

I'm using 1.5.5.1 and Avicci's one-page checkout solution.