I've found a split testing solution that lets me hide a global div element via css... i.e. adding a display: none. The experiment works on all pages of the site.

Convert Experiments: Supported! $139 per month! 15 day free trial.

Optimizley: emailed... waiting to hear back. Probably not included in their basic package.

Experiment.ly : emailed... email bounced... they want me to register now that my email is lost. Ha!

Maxymiser: no prices shown on website... I guess that means expensive.

I also searched for : affordable multivariate testing, and cheap multivariate testing, but no real relevant results.