It is possible. However, to allow a 100% up time dot for DRK to keep it would cut down DRK's dps budget which isn't that high compared to a real dps job to begin with.
Assuming Salted Earth deal 100 potency per tick that would be 100x20 tick per minute which would be around 2000 potency that DRK couldn't have for other ogcd attack,damage buff or a heavy hitting weaponskill/spell. Plus, there is no need for DRK to have a bigger and bigger *not so* greatsword every expansion if we don't have a heavy hitting weaponskill/ogcd attack at all.
knowing this if you still wish for it then here might be one of the solution:
Salted Earth now cost gauge or mp.
Living Shadow/Salt and darkness now make Salted Earth fade and summon Simulacrum within Salted Earth. When boss trying to leave your dot pool you can give it a leg and let it move to whack the boss by itself. And then after it disappear you goes back to landing you dot pool again. There, you can keep you up time of your dot and living shadow have a purpose now.