[solved] VSE API: How to create an image-strip with 1 image "stretched" over x frames

Using the VSE API I am trying to create a strip that uses one image “stretched” over several frames. As I see it, it should work via the standard images api, like this:

seq_data = ("/somedir/images/", ["0001.png", "0002.png", "0003.png"])
imagestrip = seq.new(seq_data, start, track)

what works without any problems.

Anyway, if i try to do:

seq_data = ("/somedir/images/", ["0001.png"])
imagestrip = seq.new(seq_data, start, track)
imagestrip.length = 50

I end up with a strip (of desired length) that is broken/empty/does not show an image at all. Hints?

Update:
I found it out myself! Image Sequences which contain only one image that is stretched over several frames remain imagestrip.length = 1
BUT the value that changes is imagestrip.endStill
So if you set this value to the frame where the imagestrip should end, the image is displayed from frame x to the frame you set there.