Hi Werner,
as discussed on the OSGEO mailinglist I wrote a plugin like this about two years ago:
http://osgeo-org.1560.x6.nabble.com/legal-aspects-of-QGIS-plugins-td5311034.html
https://vimeo.com/205947300
In my plugin there are some extras like progress bar and the possibility to select the North-South and East-West orientation of the stripmap polygons. Apart from that I have a second sub-tool to recalculate the angles of the polygons after the user has done his fine-tuning (moving/rotating of stripmap polygons).

If you are interested in having a look at my plugin to use parts of it I can send you the code.
regards,
Thomas