Functional software has been built and can be used “as is”:

http://www.stefanbion.de/evpmaker/index_e.htm

http://www.stefanbion.de/evpmaker/speakjet/index_e.htm

Of course we could try to build some software ourselves, using python of experimental music software.

[I also made a port of evpmaker to GNU/Linux in C: http://1010.co.uk/evp.html and also as an extension for Pure Data - http://1010.co.uk/org/software.html#sec-5 ]