Schema access in PL/PGSQL for custom objects - i.e. type access?

I was wondering how to access the schema of a type in PL/PGSQL

Basically, we've created some custom objects in the database, which
are somewhat similar to database/composite types (i.e. Create type..)-
essentially a named list of name/type pairs.

In PL/PGSQL you can define variables to be custom database types, but
when we try to do it with our custom objects we get:
ERROR: "myet is not a table"

Essentially we just want some way to create a variable (type
instance, or even row) with the appropriate name/type pairs for OUR
objects in PL/PGSQL.

Where would we start looking to 'hack' the code for this - i.e.
how/where in pgsql can i either a) add my object to be recognised as a
'type' or b) make it seem the equivalent to a custom db type

Thanks
BB