XF 1.5 xen:phrase inside a custom bbcode or a custom bbcode in another custom bbcode

Hello there,
Long title, sorry about it.

I'd like to know if either option was possible :

1- Inserting a xen:phrase (i.e {xen:phrase last_activity}) in a custom BBCode
2- Inserting a custom BBCode inside another custom BBCode

Since this is really important for me, i'd like to know if an add-on could allow one of the options if none are initially possible ?