Check out this forum post, see if it helps your modding project: http://missyhissysjobcentre.proboards.c ... 532/thread
Unfortunately, I do not know of a modder who currently takes TS3 custom careers requests, whether Rabbit Holes based or self-employed
You could also look into the code of NRaas own self-employed careers for inspiration: <a href="http://nraas.wikispaces.com/Careers%20S ... 0Eleven</a>
Finally, here is the page where to leave a suggestion for the creation of the next custom selft employed careers, I'm not sure where it's located yet on the new website at NRaas.net: <a class="wiki_link_ext" href="http://nraas.wikispaces.com/page/messag ... %20TheList" rel="nofollow">http://nraas.wikispaces.com/page/messag ... TheList</a> (hit on the "bubble" icon on the top right)
Hope that helps!
Good luck with your career creation.