Faking a TTY on a pipe/socketpair

There is a command line util (MacOS "say")* that I wish to use fork-exec'd from
my own program and send data to it via a socket created by socketpair().
Unfortunately "say" behaves differently depending on whether its stdin is
attached to a tty or not (and there's no cmd line option to prevent this).
With the former it'll speak after every newline, with the latter not until it
gets an EOF and I'd rather not do a fork-exec for each individual word or
phrase that needs to be spoken.

So my question is - is there a way to set up a pipe or socketpair** so that
it appears to be a tty from the exec'd programs point of view, eg ttyname()
returns non null?

* The MacOS speech API is Objective-C only and completely obtuse.

** Yes I know about the master-slave ptm,pts approach and I have done that in
the past but its complete overkill for this purpose.

Thanks for any help