Assuming that your BPFSL is greater than your BPEL the best way to bring these measurements closer together would be to add erect stretches to your routine. Another great way to make additional length gains would be erect expressive stretches.
You dont make your BPFSL your BPEL. You make your BPEL your BPFSL for most cases. This is because BPFSL is usually longer than BPEL but maybe your BPEL is longer than BPFSL.
Bringing BPFSL to BPEL = focus stretching on ligaments
Bringing BPEL to BPFSL = focus stretching while erect