Technically, there are infinitives that can be split - I'm thinking of the perfect passive infinitive, which is ppp + esse (to be). And if you consider those single infinitives (which I do, which makes it really annoying when they leave out the esse, which they do all the time), then the argument falls apart even more because they do split it - all the time! Technically, it might be considered a form of enthesis, so it wouldn't be a standard construction but one appropriate and standard for emphasis of certain words.

SO HAH. (I ignore markings that refer to split infinitives.)