Diamond does not have connections with Soros as far as I can find out. But Cleansweep did partner with the League of Women Voters and Common Cause - both received funding from Soros.
Common Cause is a Soros organization involved in his SOS Secretary of State project and in changing state election law to eliminate the Electoral College.
Soros Eyes Secretaries
By Matthew Vadum on 12.4.09 @ 6:08AM
http://spectator.org/archives/2009/12/04/soros-eyes-secretaries
History’s most notorious Georgian-turned-Russian, the politically astute Joseph Stalin once remarked, “The people who cast the votes decide nothing. The people who count the votes decide everything.”
The lesson has not been lost on the increasingly notorious Hungarian-cum-American George Soros.
A group backed by Soros is gearing up to steal the 2012 election for President Obama and congressional Democrats by installing left-wing Democrats as secretaries of state across the nation. From such posts, secretaries of state can help tilt the electoral playing field.
Click or cut and paste link
As I remember, LOTS of rumors about Diamond having a connection to Soros, but as far as I know, no one was able to dredge up any direct connection, just a lot of suspicions, and as you said, he was always one step removed although still doing the work to accomplish Soros' agenda.