The RCM6700 does not have PE4 available as an external interrupt. What can I do?

Please refer to the Rabbit 6000 processor manual for details on external interrupts.  There are now 22 separate pins which can be used for external interrupts.  For interrupt 0 and 1 you can also use PD0/PD1.  These pins are available on the RCM6700.  See Chapter 7 of the processor manual at this link 
http://www.digi.com/products/wireless-wired-embedded-solutions/solutions-on-module/rabbit-minicore/rcm6700#docs