making wrld_simpl longitude borders something other than (-180, 180)

Hi all,

I would like to plot wrld_simpl, but have the left and right edges of the
map be at something like 100 degrees longitude, rather than (-180, 180).

I tried messing with the bounding box with no luck.

I can imagine something like burrowing into the object and subtracting 80
degrees from all the longitudes, but I suspect there must be a better way?

Any help appreciated!
Nick