A German member of a1k.org has borrowed me his A2630, which is equipped with the expansion connector on the component side (AKA the "wrong side"). So far, all these models were considered "impossible to expand", but I had no idea why. The attached picture explains it: The memory expansion's connector would conflict with the metal cage of the CPU.
For the special version of BigRAM2630, we'll have to do some cutting on the connector. Luckily, mechanical stability of the connector won't be affected (after all, it's just a pin header and we'll be cutting on the outside box only).