The only reasons to do what you are asking is (1) to do what cpfan has stated which you really dont want to do with a Riesling as it will give it a biuttery taste and (2) for using certain fining agnets that require the lees to be stirred in as otherwise the fining agent wont work well. If you have done that and were suppoosed to stir in the fining agents then just let time clear it instead or use SuperKleer as you dont need the extra lees to use this product.
It might be a good idea to also add sorbate and sulfite at the time of adding wine conditioner. I've heard several stories of renewed fermentation in the bottle by people using that stuff. I don't use conditioner, I just add sorabate and sulfite and sweeten with sugar.
I buy potassium sorbate in powder form. I think the dose is 1/2 tsp per gallon if I remember right. You also normally add Kmeta at the same time that you add sorbate; sorbate needs Kmeta to be effective. Keep in mind that sorbate doesn't kill or stop yeast from fermenting. It only stops the yeast from reproducing. So if you have a batch with lots of active yeast in it, you'll have to wait until they finish their lifespan before you see fermentation cease.
If youve already sweetened it before adding this sorbate then Id be really cautious on bottling this as its very possible for it to start fermenting at any time. If you rack over and stabilize yoyur wine and then sweeten then I would take an sg reading when you sweeten and then in another week and if its the same then your good to bottle.