Have thought of it , but have never really decided to give it a go. I would only give the appropriate gift (chocolates , Turkish delight ... etc) at the end of the flight and ensure it was enough to cater the whole crew onboard in my cabin or whole cabin and flight crew for the entire flight ...
i would find it a tad embarrassing/cringe if someone saw me in the act of giving the gifts - that is maybe just me thou ...
I prefer to give gifts of appreciation via the compliment form on BA.com via the saying thank you form ...