I recall submitting an enhancement request for something similar to this a while ago. It's likely on a list somewhere to be "looked at" but no idea if it will be adopted.
You cannot add flanges to curved edges so you need to create straight sections where ever you want a tab. That will likely change the tube from being completely round to something that is a combination of curved and straight sections. Not very good looking but it will flatten.
Another option would be to use Configurations; one with the tabs in the unflattened states and following the curvature of the tube, another config with the tabs as PART features showing them in the formed state.
Which version of Alibre are you using? And what are the dimensions of the pipe that you are working on? I might be able to work up a sample for you in v25 or v26.
Here are some screen shots from v26"
And a Flattened part: