No, only dealer upgrade.

You could order an 8MB Mac II and 4MB Mac SE (for a period), but Apple were bitten by RAM prices in the 1980s. At the time, it was difficult to buy 30 pin 1MB SIMMs at a sensible price, but Apple could get them. Apple didn't gouge on RAM prices and their upgrades were often cheaper than third party suppliers. Many people bought a "high end" Mac with lots of RAM. You took half of the RAM from one Mac and put it in the Plus (or 1MB SE). Then you put the 256KB SIMMs into your new Mac.