Found this out by accident while playing yesterday and I couldn't find a thread on it. The method can only be used to get the creeper skin or the random ms. splosion one.

-Download the skin pack 1 trial
-Go into the skin change menu
-Hover over the creeper skin
-Press left on the D-Pad and while the skin is moving left to the wizard one press A
-You now have the creeper skin for free.

This can be done moving right to get the ms. splosion one. I have attempted methods for getting other skins however they haven't worked. There may be a way to get the other locked skins using save editing but I have no experience in that.