At this time Inventor Sheet Metal can't easily design or manipulate parts like this since it requires manipulation or stretching geometry of the material, which Inventor Sheet Metal can't solve, it's really only meant to create more simple bench-pressed parts.
However there are workarounds, do you already have working designs or flat pattern solutions in Autocad? I've found that making two parts with parametric links or using multi-body sheet metal design is a good solution since you'll essentially have one part as the folded model to use in assemblies and drawings, and the other part to make the flat pattern. It may be possible to just make the necessary manipulations to the flat pattern, but that can be very tricky and unstable.
If I have time today I'll try to come up with a sample of what I've done in the past to make these parts, good luck.