One way is to sacrifice some of the Flex sensors and position those inputs to collect ECG or EOG inputs. You may be able to attach a custom-made lead into the Flex sensor socket (for example, wrap a felt pad in foil and solder a standard lead for disposable stick-on sensors onto the foil). 

The ECG / EOG signals will be recorded on those channels, sharing the same referencing and time base as EEG. Large, rapidly rising signals may be slightly distorted (there is an built-in slew rate limit of 65uV/sample - signals changing faster than that rate will be limited) but the overall waveform shape is retained.

Another option is to use the marker system in EmotivPRO to occasionally synchronise the two time bases. If your recording software for the other devices can generate outputs you can use that feature to send markers which will appear in the EEG stream.

Lab Streaming Layer (LSL)