I see modifying standard pitch cogs to run on a skip tooth as a stop gap. If you do it reasonably well, it will function, but you may see accelerated wear on the cog, chain, main sprocket, or all of the above.
A conversion cog, at least a decent one, will have a different tooth profile and thickness suited specifically for skip tooth use. Ichibike had a bunch of them for awhile, but others may be making them. You'd have to check with them if they have any more. They're worth the money, in my book at least. There's definitely a market for these parts to be made.