I have been in this situation before.
It was in a ACS tourney I was in this past may. I was stripes, he was solids, I had all my stripes off the table, he had 1 solid left, it was a race to 7, I was 6 he was 3, he took a time out to use the rest room, when he came back, he got down to shoot the 8ball. I couldnt say something fast enough cause I had a bouth full of water and I threw my towel at his back. He turned around pissed as you could get. I told him he was solids and had 1 ball left to shoot......he called me a smartass. he won that game, but I cam back to run the last rack to win the set.....I told him I wasnt trying to be a smartass, I just didnt want him to foul by shooting the wrong ball and giving me ball in hand on the 8....he stated he wouldnt have said anything to me..I just told him I would have felt bad if I had beaten him with me having BIH on the 8.....
I would even do it in a pro tourney...I just think its the right thing to do...