We pretty much do that now.
If you go to the advanced options, then click the stacking tab. Click add stack, choose stack size, click add all.
This will use the best stack it can. The real power comes when you are trying to stack multiple teams, you can simply click add stack again to add a second stack, choose stack size and then click add all. So for example
Will set it up to use 4 players from 1 team, and 4 players from another team. You could also set it up to use a 5 player stack with a 3 player stack, or you can add a 3rd stack and use 3,3,2
This is a pretty powerful and flexible way of creating stacks. This will also only use players in your pool, so if you have the pool narrowed down that will be accounted for. Hopefully this works for you, let me know if you have any questions or if nay of this doesnt make sense.