An alternative route is get rid of the series pot at pin 1 altogether, put a 10K pot in series with each of the two diodes, and replace the existing 10K pot with a short circuit. The duty cycle adjustment will not be independent of the frequency adjustment, but the ON time of the pulses is adjusted with one of the pots, while the OFF time is adjusted with the other pot. So, at least, the ON time and the OFF time are independently settable, allowing you to adjust the frequency and duty cycle.