It is always preferable that you leave such things for the bar manufacturers to do, but if you are careful to drill the smallest holes for the cables and "ease" the holes so there are no sharp edges and burrs that coils cause a stress riser on the aluminum tubing, you could be OK..... but no guarantees!! though. You can also consider getting handlebars with grooves on them for the brake cables to sit in so they will be flush when you put on the bar tape. Pretty much the same results as when the bars are drilled for cables....
Also realize that once you drill that bar, considered its value ruined for good.....