How can I add two or more edge flanges to a part each one with a different length?

Here's an image of what I'm trying to do:

I need to add A and B edge flanges. If A and B have the same length, solidworks does  the job in a blink of an eye.

But I've been trying to get an acceptable result when A and B are not equal for hours and still I have no clue how to do it.

I've attached a file in case you need to do some tests.

In the attached file I need to add 3 edge flanges as the following image.

A=12mm

B=18mm

Any kind of help or advice is much appreciated.