Set the end of a composition with expressions

We use a lot of AE automation.

End titles can vary in length.

We can't adapt the length of a render range to the length of the content we have.

This means end titles always have to be the same length like 1.5 minutes to guarrantee all names will be in there.
This however, poses problems when the endtitles have to be started in a live situation: the operator either won't know when the content ends (when you composit from the beginning) or begins (when you composit from end to begin).
Rendering exactly to length with help of an expresion would very much help prevent many problems. At least the End point of the workarea should be possible to set with an expression.