====Allow invasion to homeland====
A bit risky option is to cancel all forts (including Labourd), not to call Castile (or any other allies) early on and allow France to occupy quickly the mainland. England's navy is superior but should not battle the French navies (at least not the transport ships) and concentrate only on Scottish' one. Once the mainland is occupied, France is seeking for another lands to be occupied and will probably invade England. Invading armies are however small (probably around 10k stack) and can be completely destroyed quite easily as they have no chance to get back to France. This can provide warscore, army tradition and decent manpower/money reduction on French side. Once the invasion is repelled, allies can be called in and French navy destroyed. In this case 30 months period
mus be kept in mind as afterwards the allies can't be called in. Risk is that the allies could be in another war meanwhile meaning they are not willing to join you.
Alternative to this is to allow them to invade, destroy their navy without destroying the armies, move English forces into mainland and call in the allies. This divides French armies allowing the allies siege down the mainland more easily. With some luck half of French army is locked in island and can even defeat the potential War of the Roses rebels.