Cranberry addition to secondary

One of my holiday beers I'm brewing is going to be a cranberry wheat. My question has to do with cranberry additions to the secondary. I brewed a basic wheat beer (it's in the primary right now) and plan on adding cranberries to the secondary. I'm going for more of a sweet cranberry than a tart taste, so I've decided to use a mixture of frozen cranberries and cranberry juice concentrate. The plan is to make a cranberry mash and toss it in the secondary fermentor. All the recipes/advice I've read has been basically "add to taste", how the hell do I know what the final taste will be when I'm adding to primary?

Has any done something similar with creating a 'fruit slurry'? How did it work out?