Pausing during in-app purchase

I am wondering if there is a way to pause the game or wait until receiving the validation callback from a purchase.

Currently the only way I know to pause Unity is:

Time.timeScale = 0.0f;

Unfortunately this doesn't pause the game, it only stops the Monobehaviour updates, and has no effect on any GUI items or elements (which is beneficial for a pause menu, but in this case, the GUI shouldn't be able to spam purchase calls when still waiting for a previous purchase to validate).

I was hoping there was some sort of access to an iPhone specific pause function or something, but have been unable to find any information on this.

How do the rest of you guys do this? Clearly there are other Unity-iPhone games that have in-app purchases, how do these games handle waiting for a validation from the app store?