I'm a leftie and I've always liked it except for the smearing while writing thing.
I played violin when I was in school, I did have a left handed violin and the teacher just used the mirror method.
For guitar I would suggest trying the regular way to see if he can learn that, if not you can buy leftie guitars or just reverse the strings and use the mirror method.
Kurt Cobain and Paul McCartney both played left handed guitars and I'm sure there are many other too.