There's a design of a home made jig that works pretty well with scary sharp. It is shown in the book Hand Tool Essentials. There's a good chance that is a duplicate that has been in Woodworking magazine some where.
Personally, I just do it free hand.
I cant' find the story on the Old tools group that made me decide to do it but it went something like this "A guy was hanging out with his FIL who was a well known, high quality furniture maker. His plane got dull, and the guy figured he would get to see how a pro sharpened his tools. The FIL popped the blade out, spit on his sharpening stone, rubbed the blade around a bit, did the back, then popped it back in and kept going. The guys asked the FIL why he didn't use some fancy jig. FIL replied "Some people like to play with their tools, some people like to make things with them"
That was good enough for me.