[CydeWeys]

My interpretation was that it can only be set either on the exact hostname that was loaded, or on the second level domain name that was loaded. To set it on 32 different SLDs you'd have to redirect through 32 different domains, which the user would notice.

Note that this is for the page that was loaded only, not for additional resources hosted on other hostnames.

[Karliss]

Redirecting 32 times could be made less obvious by opening a small popup which closes after finishing it's work. It used to be possible to open a popup in background, that would have made it almost practical.

[JetSpiegel]

Or just an async script?