Remote fill master cylinder

[mrjs80]

So I want to do an under dash master to clean up my firewall. But that includes it's own set of problems. You have to be able to access the master to fill and check fluids. So I was thinking the best way would be a remote fill reservoirs. There are a few companies that make them but they either have a single reservoir or they don't have the bore size I'm looking for.
I was wondering since I already have a master could I just tap, weld, glue, etc a fitting to my existing cap? One for each reservoir, then cut the middle out of the rubber seal so the fluid would actually get to the plunger. The perimeter of the gasket would still seal the cap to the master. Then just run my lines to where I want (I was thinking under the cowl) and use an aftermarket plastic reservoir.
I really don't see any difference between that way and say Wilwood's way. The only difference that I can think of would be the amount of fluid. You would be filling both the new remote reservoir and the stock one. More fluid shouldn't be a bad thing?
would save some money