Actually, lamb stock can be used for sauces... for lamb, of course.
The problem is the smell, and the main way to get rid of that is to get rid of the fat. The best way is to roast the bones and meat, after first trimming thoroughly. As you make the stock, SKIM SKIM SKIM -- there's less leeway here. Make it strong: either you want that flavor intensely or you don't want it at all, so reduce if you have to -- it should gel lightly when cold.
Don't store it too long, either. I'd give it 1 month in the freezer, tops.
To make a great lamb sauce, combine 500 cc strong brown lamb stock and 1 bottle decent Merlot (you'd be willing to drink it). Bring to a strong simmer, skim very well, add 2-3 cloves crushed garlic, several cracked peppercorns, and 1 fresh rosemary sprig. Reduce heat to a gentle simmer and let cook until reduced 50%, which will take an hour or more; you can do it faster, but for some reason it doesn't taste as good. Strain very fine, then reduce relatively rapidly by another 50%, until thickened to sauce consistency (it should nap a bit). Mount with 3-4 Tb butter and serve with (for example) herb-crusted rack of lamb.
Add a side of garlicky white beans, a salad of good bitter spring greens, a loaf of crusty bread, and an excellent Merlot to drink, and you've got a meal to remember.