There's a fundamental difference between bending text to a path and using a distortion envelope. As Fred noted, only text contains sufficient information to force it to an arbitrary path.
Whereas a distortion envelope remaps each and every point within it thus creating the distortion. It makes no difference if those points are text or just vanilla paths.
Flexi's distortion envelope capabilities are rather primitive but you can often move individual or related pairs of envelope points by using the shift and control keys. This works on some points on some envelopes, not just anywhere. You have to mess with it a bit.
Corel on the other hand features a truly civilized distortion envelope capability. There you can create most any arbitrary shape with any number of points as well as use, and modify, any of its three canned formats. Corel's envelopes are adjusted in exactly the same manner as any other path is shaped. Flexi isn't in the same universe vis-a-vis distortion envelopes.