I really don't see this as a possibility. All those ores you suggested that would make it already have a chance to give Diamond so why not just aim for the diamond, like you're already there mining the ore.

I think the players that have collected their 100+ diamond for their characters or friends will be rather peed off knowing players want a simpler way to get it. It's not meant to be a easy item to get and players have collected it as it is meaning it's do able, it just takes time.

Oddly enough I just typed up a suggestion to this I'm going to post in a moment (actual plan of action). But yes, mining is doable, but very very very very few actually mine it all themselves. Most buy some if not all of the ore they need. And as those who do mine it complete their characters (or buy) [and many do more than one character] there are fewer people to mine for ore (or to sell on the market). Another issue is... majority of the time the rest of those non-diamond ore's go to waste.

The major problem with having a recipe or something similar though is that it is hard to balance the difficulty in obtaining higher quality ore to where it isn't too hard or too easy that it throws off the balance of pure diamond ore mining too much (current system). It is nice to make it a little easier, but if it becomes too easy, it will destroy the value of diamond ore in the economy. Anyways i'll go post my idea in a new thread in a moment.