It's not really "2-stage fermentation", and you don't really "need" a secondary tank, but it helps. The term "secondary fermenter" is a misnomer actually. There's really no fermentation going on in the secondary vessel. It just allows for some bulk conditioning, as well as for more solids to fall out of suspension resulting in clearer beer. But even a belgian dubbel can be done without a secondary.
If you were to secondary in your bottling bucket, then once you added your priming solution and stirred the beer, it would rouse all the sediment that had been falling out of suspension and cloudy up your beer again. You COULD do it without any extra equipment, but there'd be one extra racking step, which increases your chances of oxidation and contamination. But it could be done:
- Primary fermentation in carboy for 7-10 days or whenever gravity stops dropping.
- Rack to bottling bucket, age for 2 weeks or more.
- Rack back to original sanitized carboy leaving the settled trub in the bottom of the bucket.
- Clean and sanitize the bucket, add cooled priming solution, rack beer from carboy back into bottling bucket for bottling.
It's kind of a roundabout way, but it'd work. Ideally, you should have a dozen carboys and/or buckets, like I do.