There are some finings used in brewing that might work as well or better than the agar used in the article linked above. The natural ones are either gelatin or isinglass, but putting horse hoofs or fish bladders in a juice just doesn't seem right (even if it settles out). There is an artificial fining made from some sort of plastic (I can't remember the name). I wonder if some of the bio-engineered enzymes might work, like Brewer's Clarex or Crystalzyme (made by DSM foods and sold by White labs). I read that these enzymes exhibit pectolytic properties in acidic juices, but work much faster than pectin. They are derived from black-mold which I find a little alarming, but are used by some commercial microbreweries and are certified for food use (and kosher). At least they are not genetically modified. Crystalzyme is a fungal enzyme engineered specifically for aiding in the clarification of acidic juices. I would do a little research first, but these enzymes sound interesting, maybe used in conjunction with a juice press.
http://whitelabs.com/enzymes/Crystalzyme.pdfedit:above I stated that Crytalzyme is made by DSM, but it is actually made by Valley Research