Skip all the below and search "coloured coins" and/or "colored coins", colour some coins and you're good.
Or read on:
It is easy. Simply convince 51% or more of miners to merged-mine yet another chain.
Currently the maximum number of chains being merged mined by anyone I know of is only seven: BTC, NMC, DVC, GRP, IXC, I0C and CLC.
(I had to stop trying to add geistgeld to the merge for now as it was too resource-intensive, interfering with my machine's ability to handle the others well. More machines might fix that but will/would cost more electricity.)
So the most useful first step toward your goal would be to work on getting more miners to add more chains to their merge, since until they all see and experience as fact that merging seven at once works fine there is no point trying to add more to the list.
For people in a hurry and not too worried yet about attackers, GRP is still looking good because it is insanely low difficulty still, even CPUs can mine it, so it is basically so incredibly dirt cheap to mine it again makes little to no sense to try to add yet another to the list when this one is sitting there ripe for the taking even by people who only have CPUs.
It also serves as a weather-vane to all the many chains that are waiting in the wings, especially the ones that moved to the Open Transactions platform in order to establish transaction volume sufficient to attract miners before attempting to go public in blockchain form once again. Basically if you can succeed in getting enough miners to merged mine GRouPcoin to make it secure against attack, then entire groups of chains who are ready to come out of the closet the moment miners become open to merged mining more chains can do so. If they too can also get enough miners merged-mining them to render them too secure, then possibly we will have proven that spawning even more is reasonably do-able.
Meanwhile proving on some other platform that you have enough transaction volume to make your currency attractive to miners could also move you along toward your goal. Open Transactions is probably not the only platform you could use to get your economy up and running and thriving sufficiently that it reaches a point at which the cost of paying miners so you can reasonably move to a blockchain format is a reasonable overhead cost compared to the sheer volume of sales / transactions / activity going on in your currency's economy.
Take a look at
http://galaxies.mygamesonline.org/digitalisassets.html to see how some of the currencies working their way up in non-blockchain form toward a point where going back to being blockchains (as they were originally and as they were designed and intended) are doing toward that goal...
-MarkM-