Even if you could (which is very questionable), you would have much more work than doing it in standard mode with solid features and no benefit, as it would never unbend in any way.
There are too many details which deviate from the sheetmetal idea (constant thickness, tangential transitions) - rounds, the triangular cuts, etc...
Note: Just because a part is machined out of a sheetmetal workpiece, it does not yet qualify for creating it as a sheetmetal part. There should be mainly bending processes instead of forming/forging to justify using sheetmetal - which is definitely not the case here.
If you are (in your real-world-process) bending the base of the part and add the details by machining (e.g. mill the rounds and the triangular cuts), then you may consider modeling the base part as sheetmetal and then add the details to a standard part that copies the geometry from the sheetmetal part.
Interesting design. I suspect you can do this in sheetmetal if you do as Gunter suggests, make it all one common thickness. You may be able to do a reasonable flat pattern. You would then add the part to an assembly and do the secondary machining operations. The only place I can as a challenge is the S-flange off the 1/2-curve surface. It can be done with a form, but that doesn't give you an accurate flat pattern. Maybe a S-shaped flange.