I have a Kiniki Brazil Swimbrief Bikini:
http://www.amazon.co.uk/Kiniki-Brazi...G4XYWFYPM9R N
It has a men's Brazilian cut at the rear and a crotch seam wide enough to be pop out free. The crotch seam is 2.5" (6.5cm) wide. they have achieved the cutaway rear by making the bikini high waisted and narrow at the hip.
Kiniki have a reputation for being somewhat old fashioned, I suspect that this is not the suit that you want. The modern look has a lower waist and may be a wider seam at the hip. Making these changes would lose you the Brazilian look. The women's suits that you like achieve the Brazilian look by having the very narrow crotch seam, which you cannot use.
Designers of male swim thongs have the same problem, the narrowest part of the rear may be only 0.5" (12mm) wide the width of 2 pieces of elastic side by side, but this is widened to 1.5" (36mm) at the crotch seam and the front of the suit widens rapidly from the seam.
In conclusion what you want your designer to do is bring the rear of your suit towards a point at the base of your buttocks and then widen it out again to meet the front of the suit as it forms a pouch. the result would be a safe masculine modern Brazilian.
I almost want to make one myself. Happy days