My favourite ENTJ does something designed like that and it seems to work.
How do u do it?
1) When INFP is sad and tells u about their problem, be very interested, but pretend that u don't see where the problem is.
2) INFP will get all flustered and angry trying to convince u about the danger and gravity of the situation.
3) When they are more angry than sad - shout "Ha ha you are not sad anymore - good." And then prove that u understand the situation by summing it up.
4) That way INFP feels that somebody understands their situation, but doesn't have that heavy sad feeling about it and has energy from their anger.
It works wonders for me - things don't seem to be so desperate after that.
Still handle with caution - red trail for experts.
Still 2 - none of the experts was born one - u need to practice.