C# - Set Recaptcha Key Settings At Runtime?

I'm implementing the recaptcha control from google.

I built a simple c# test project from their example and all works. Now, instead of having the PublicKey and PrivateKey in the aspx page, I'd rather assign these values at run time as they will most likely be pulled from either the web.config or a database table.

I tried the following in the Page_Load

protected void Page_Load(object sender, EventArgs e) {
recaptcha.PublicKey = "<deleted for obvious reasons>";
recaptcha.PrivateKey = "<ditto>";
}

but I get an error stating "reCAPTCHA needs to be configured with a public & private key."

I also tried overriding the oninit method of the page and assigning the values there, but no joy.