Sure you could. At a minimum, all you need to do is go to a rock shop, buy a piece of uranium ore, a piece of beryl, and touch them together. Note that nature has already performed this experiment - uranium ore typically contains ~1-10 atoms of 239Pu for every 1012 uranium atoms as a result of capture of stray neutrons (from spontaneous fission of 238U, cosmic ray spallation, etc.) by 238U, so if you just want a trace amount of Pu you don't even need to make it. This raises an interesting question - at what rate does the concentration of 239Pu in uranium ore decline? Since this depends on both the concentration of 238U and the stray neutron flux (which itself at least partially depends on the 238U concentration) it should decrease faster than that of 238U itself. Has anyone figured this out?