I don't really see the use in it to be honest (the whole point of BeebAsm is to help you
avoid the emulated BBC environment!), but also it'd be difficult for larger projects, where the problem is always about dividing memory between source code, variables, and object code, all in 27k of memory!
But I'm intrigued - what do you possibly have in mind that would make this a useful feature?

Incidentally, I'm reasonably sure that, given the very similar syntax to BBC BASIC, you could probably approximate this with a clever (and very lengthy) regular expression (to add header and footer to the program, and to convert the BeebAsm commands into their BASIC equivalents). But I won't volunteer such a behemoth myself
(Have a great trip if you've already started on your way...)