While it is understandable that you wish to avoid breaking concrete, there is really no alternative. Any attempt to make something up will never be satisfactory, and the last thing you want is a toilet installation that causes problems. A good toilet when properly installed will last virtually forever with nothing more than new innards occasionally so you certainly would be "penny wise and pound (dollar) foolish" to try to hack something together. There are a couple of options at least for doing this. You could rent or buy a small rotary hammer/drill and DIY. It's a dirty job, but doable. You could let a plumber do it, but even if you found a plumber who would do it, that would be a very costly job. What I would suggest to you is to find a company in your area that cuts concrete. They won't be cheap, but it will be quick and clean. You will still need a plumber to do the plumbing portion, so there will be considerable expense for the total job. Need I say that the project should be topped off with a Toto?