Technically, when attempted in game here it appears to be possible.

The closest thing I could find was in the support section of the 2008 edition rules. It say's "The province to which a unit is providing support must be one to which the supporting unit could have legally moved during that turn." Technically, a fleet in Marseilles cannot move to the north coast of Spain, so I'd think this would be specific enough.

It also says "A fleet that can move to a province with two separate coasts (a fleet in the Mid-Atlantic, for example) can support another army or fleet into that province (in this case Spain) without regard to separate coastlines."

For some reason there is no specific example that applies to this. Although in the DATC tests for this site there are two examples without pictures:
6.B.4 - Passed
TEST CASE, SUPPORT TO UNREACHABLE COAST ALLOWED
Thinking about them hurts my head, but I believe that this case means that Marseilles would be allowed to support Gascony to the north coast.
6.B.5 - Passed
TEST CASE, SUPPORT FROM UNREACHABLE COAST NOT ALLOWED
The second case seems to imply that a fleet on the south coast cannot support a fleet in Gascony?