Well, I'll preface this by saying my BSR4EG fretless is the most comfortable and best playing bass I've ever touched.
Having said that, the only thing I could think of that would improve the comfort a little would be to shape the top edge of the body where the forearm rests so the body is thinner there. The downside to that is it could impact the tone of the bass, and definitely would impact the look since it's a multi-layer body.
It's rounded already, so it doesn't really hurt, but I've found that on some of the longer sessions I've played, my fingers can start to go numb from the pressure on that one spot of my forearm.
Given the impact this change would have on the look of the bass, and the potential tonal impact, I wouldn't really change this as it's not that big of a deal. But, when asking for constructive criticism on perfection you should expect things like this
