I have pdf2ps on my machine. According to its documentation, it is a wrapper around gs (aka ghostscript). Taking a look at the documentation for gs, it looks like it will happily take input on STDIN and send output to STDOUT. (It says that it wants a switch to tell it that STDIN is coming on a pipe so it changes its default behaviour about when it has received all of its input.)
I haven't played with it, but this makes it look like you can develop versions of both utilities that operate without any temporary files at all.