you can 'cheat' and double / triple your custom islands, by
doing something like
----
content island x
{$tbclose}
{$tbopen}
island y title (use rightheader or left)
content island y
{$tbclose}
{$tbopen}
island z title (use rightheader or left)
content island z
---
that does 3 in 1. one limitation is that every time you do island x, you always get y and z