Hallo noch einmal Nils!
The Living Rules "Word" version includes the following "experimental rule" (5.4C):
5.4C Experimental Rule (WT as cargo): You may load WT onto your rocket stack as “cargo”. For each WT loaded, place 1 clear disk on your rocket stack, and increase the dry mass by one. You may convert WT cargo into a fuel tank or into a WT at LEO as if refueling at LEO (above). Rockets can use the Site Refuel operation (5.5A or 5.5B) to add WT’s as fuel or cargo in any combination. This applies to atmospheric refueling (6.4F) and dirt refueling (8.3E).
My reference is: HighFrontierLivingRules_Apr_02_2011.doc found in the Yahoo Group http://games.groups.yahoo.com/group/HighFrontier/files/
Unfortunately, the experimental rules did not make it into the published second ed rules because of space reasons.