basically no you cant have a permanent guardians pledge up constantly at the moment,
You can reduce the cooldown on the skill though in 2 ways;
1- Legacy on weapon which gives 60 second cooldown
2- Set bonus on the ToO armour which also gives another 60 second cooldown
So that at least takes the cooldown down to 3mins instead of the usual 5.
Heck with constant guardians pledge We would be nigh on unstoppable.. hehe We can dream that it will happen in RoR expansion though :P