Two ideas, and both require being able to scrub off all offensive weaponry first.
Use large numbers of marines. If you can demonstrate a credible threat, you may get the station to surrender without having to actually put in an assault.
Actually assaulting a station would depend on a number of variables; tech level differences, station layout, number and quality of defending troops, etc.
The second option requires time, possibly lots of time. Scrub off the weaponry and wait.
Maintain a ship near the station to conduct harrassing fire and launch raids with marines to damage or destroy any facilities that enable the station to hold out; like food production and atmosphere control.
If the station uses sun shields to block excess radiation, you could damage or destroy those. Repairing them afterwards should be simple and the threat of being cooked in their can might get them to give up.
Eventually, they may give in, but sieges can last a long time, especially if the defenders are well-prepared.
Alternatively, threaten to destroy large population centers on the planet. It's messy, has no guarantee of success, and you might be opening your own worlds to the same threat.
edit: This was suggested to me by a friend:
Pre-invasion commando assault. Send in marines on a Trojan Horse, like a large freighter. If they can dock or get close enough for an EVA assault, they might be able to disrupt the station and hold out until the fleet arrives from jump and clears the opposition away. Something like
Pegasus bridge.
In order to work, this would require some fairly lax security on the station, but it's certainly more interesting as a game than a long siege would be.