Personally i dont recommend widening alloy wheels via welding, as the composite of the alloy will never match 100% the weld, and will create a weak point in either the weld or the fusion point of the weld to parent material
With 3 piece rims id look at finding some 3 piece blanks that can bee drilled if poss before welding
3 piece wheel bands
Re: 3 piece wheel bands
vr6 idea still siting there, much research in the plumbing before I commit.