Thanks to the guys at Zone Five Software for their support; really appreciated your extensions to the API.
Thanks to Neil Catley as well, who has been the real catalyst here. Neil first put a video on youtube to help others upload manually, then asked for a more direct integration. That's the spirit :-).
Just like with Garmin Connect, at the end of the upload process the app shows an hyperlink, so that you can jump to the activity on sporttracks.mobi with one click (Uploader 4.4 and up, Sportablet 5.6 and up).