You could get an injunction to specifically prevent them moving any BTC from certain addresses (technically they aren't supposed to move anything at the moment anyway).  You could ultimately seek an order to have BTC from those addresses transferred to an address controlled by the supervisor/investigator. 

It all depends on how willing MtGox is to risk being in contempt of court and how long it might take to get such orders - and whether you can prove that the addresses belong to MtGox (they shouldn't be "frozen"  or seized by any means unless substantial evidence of them belonging to MtGox, Tibanne or Mark can be demonstrated).