bash script to display words in parentheses

I have this:
var="I said ( hello world ) and the world said hello back."
var=${var#*(}
echo ${var%)*}

which outputs:
hello world

as expected.

However, I am trying to simply turn that into a one-liner which I've
been completely unsuccessful with.
The reason is that it has no significant advantage currently over cut/
awk/sed solutions as the variable is being re-defined. Does anybody
know how I can turn the above into a one-liner?

The following command (and many other variants) do not work:

echo ${var#*(%)*}

Any help would be much appreciated. Thanks.