Both tanks take tethers during P2 so cannot have other tank take it, both need to mitigate through it.

While the easiest solution is have 1 tank invuln tether, other uses some mitigation, then on P3 tethers, other tank uses their invuln and while you kitchen sink where blocking will work.
Of course, OP said that isn't an option, so guess they'll have to make do without blocking under the effect of down for the count.