Stumbleupon have a url shortening service: su.pr
they also have a plugin for wordpress that lets you shorten your urls.

if you use the ‘supr by stumbleupon’ plugin in your wordpress then it will auto submit your posts to stumble upon!!

to set it up:
first head over to su.pr
sign in with your stumbleupon details
then go to settings and copy your API key.

in your wordpress goto plugins > add new
search for ‘supr by stumbleupon’
install it, activate it and paste in your api key and username from spur.

there are a few options here for you to play with, such as auto post to facebook and twitter aswell :)