as tank is running use quelling strikes and the problem goes away as you'll start thunder 2/3 straight after, with it hitting as tank hits its first target, then fire 3, either tank has at least 2 hits by the time fire 3 hits and are on there way to generating more hate on the whole group or single target.. blm should not have to hold back at all.
of course you have to correctly identify the tanks target as he is running to precast thunder, but my guess is closest enemy to him/her 99% of the time.
I say this as a blm main who tanks more I think lol.
if the tank cant hold hate from that point its on them, heck a blm shouldn't even need quelling strikes at that point but at least there doing there part to help the tank.