It's a major pain the !@# and a very real nerf in GCD efficiency as is, but you no longer have to deal with it.
With using the following addon and macro combination you can continue using PW:S as normal.
First, download and install the addon below.
Second, make the following macro and bind it to your PW:S key.
/cast Power Word: Shield
Third, grab a beer and mash that button all you want without your UI trying to get you killed by the Horde.