Just buy a different master cylinder with lever.
You don't really get anything out of just changing the reservoir but if you get a radial mount master cylinder it will improve braking.
Stock newer suzuki gsx-r models are radial mount - Good upgrade for cheap cost.
http://www.ebay.com/itm/11-SUZUKI-GSXR750-GSXR-750-RADIAL-FRONT-BRAKE-MASTER-CYLINDER-/180746482727?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item2a15547427
I've got a few R6 ones laying around that are radial mount as well. Anything 2003+ will work.
Or you could get a brembo...one of the best upgrades on my racebikes I ever did.
http://www.yoyodyneti.com/ProductInfo.aspx?productid=10.4760.80
I've got a 2009 r6 one on my x - ill try to get some pics