He was able to get them to the Parliament and to the government. He would never agree to join a government with the social democrats because such a coalition would have to be supported by the communists which he would find unacceptable. Instead, he chose a government with two conservative parties - libertarian ODS and the Christian Democrats - because "conservative" means "cool" and "progressive", at least in the Czech Republic.
The foreign minister - chosen by the Czech Green Party - supports the radar base in the Czech Republic and the meeting of the Czech Green Party took a neutral position and didn't even support the calls for a referendum about this question. The German Greens understand that Bursík's successful strategy was to avoid being a fringe party - and in the post-socialist world, fringe means left-wing.
Needless to say, there are also leftists in the Czech Green Party but they realize that without the centrist leadership, they would continue to be irrelevant water melons: green (environmentalist) on the surface and red (communist) inside.
Well, I happen to think that Bursík is not particularly green in any sense. He just realizes that there is a political demand for the green ideology but there are no good politicians in this field because more or less everyone who really believes these green things is a moron, so he benefits from this opportunity. ;-)
See playfuls.com.
Another news from the Czech politics: it seems very likely that BAE systems has paid huge amounts of money in bribes back in 2001 before Czechia decided to buy supersonic Gripens from that company...