There's probably a few ways to go about this but I'd be tempted to simply cut and scoop into a large, sanitised and weighted grain bag (or go naked if you have a way to filter pips out after) and add to the FV just after high kraussen. As for how much, not sure, depends on the flavour profile probably, but in a recent raspberry IPA I used just over 2kg of raspberries, you probably wouldn't need to go that far though. Also, don't take my word for it, look up some recipes and techniques online..