I haven't found a way in either. If you start your own company somewhere in the field, or otherwise support yourself, you can rock and roll as an indie researcher. Otherwise, a Ph.D. seems necessary.
I wonder if this will change over the next decade, as synthetic biology continues to expand rapidly.
Also, beware the "$TOPIC is expanding rapidly" trap: synthetic biology is merely the buzzword of the moment. When I started, it was computational biology. Later, genomics. The number of opportunities created by these booms has never kept up with the hype waves that preceded them.
[1] There is, however, a pathway for "business" people who enter biomed. But I'm assuming you're not interested in this, and in any case, getting a PhD won't help you with it.
The roll-your-own-company lab approach sounds a little better, overall. One tricky thing is that I'd have a lot more credibility starting a biotech company with a Ph.D. Right now I'm considering a Ph.D. to get the training and credibility (union card, as someone else said). Still not a slam dunk, though - Transcriptic's founder just has a bachelor's.