Speaking of Dwarf Manager, you are using it right? Because I don't think I could ever handle more than 7 dwarves without it.
Remember, the skill the dwarf comes with does not mean they have to do that job, merely that they already have some skill at it. A fish dissector can do masonry, and in a week or so he will be better at it than he ever was at dissecting.
I usually use my immigrants to create large constructions, and to haul out the stone that my 8 legendary miners produce. This is a full time job, and even with +120 dwarfs there is always a shortage of labor.
Try turning all your excess migrants into masons, then build a giant multi-level wall around part of your outdoors. Not only will it give your dwarves a safe outdoor place even during sieges, but it will consume vast amounts of stone, especially if you put in floors.
Right now I'm solving my overabundance of stone by having 80+ dwarves building a giant rock tower to store it all in, and then they will spend another few years hauling stone into it. If they ever finish with that, I can build another one next to it! I have 8 legendary miners, so there is no shortage of material. See
megaprojects for more creative ideas.
Stone detailing can also keep a lot of dwarves busy for a while.
If all else fails of course, you could always set up 4 stone piles that "Take" from each other in a circle, causing dwarves to haul eternally.
Finally, if
that fails, put them all on
excercise bikes.