Contributed by Russell Coker on Debian Bug#126486.

/etc/pptp.conf:
option /etc/ppp/pptp.options
localip 192.168.236.133
# refer pptpd to use the pptp-portslave script instead of regular pppd
pppd /usr/sbin/pptp-portslave

/etc/portslave/pslave.conf:
# configure it as usual, but with lines defined for pseudo-tty devices
s{1000-1063}.tty   pts/{0-63}