You can simulate this with so-called "Bernstein chaining". Basically, each program takes another program as an argument, and finishes by calling exec() on it rather than exit(), which preserves the environment. See:

http://www.catb.org/~esr/writings/taoup/html/ch06s06.html

Or write environment variables to stdout in Bourne shell syntax so the caller call run "eval" on it. Like ssh-agent, for example.