The concern about stretching "causing scarring" appears as a common mythology even among some doctors it seems - strange considering that urologists in particular actually perform procedures in which they dilate the urethra well beyond the level of comfort (thus: using anaesthesia). This is a gross confusion of cause and effect - stretching techniques are commonly required in medicine to treat conditions caused by scarring, the stretching is not what was responsible for the scarring.
In this case, any disease (as we discuss) which causes scarring, makes stretching more difficult and demonstrates as fissuring, but the fissuring is strictly a manifestation of the disease.
It is the case that techniques (as are used medically for "skin expansion") employing less force but applied most or all of the time are the most effective. Having only one hand free is clearly a major limitation but until that is solved you might look into using some sort of "device" to stretch - for much of the time - without even needing your hands.
Stretching by retraction only will be effective to some extent - after all, it is how the foreskin naturally becomes retractile in the first place - but will try your patience.
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