both of you post LFG in chat and stay together instead of being in a group. Or just post looking to merge groups or something like that. Although i dont lfg so im no expert >_<.. you could aslo post something like " 2 people lfg, whisper me and we will disband and join yours"... Or you could always start your own group and have someone else lead it
Depends on what server you play on, you can always
LFG and get picked up by a random group
LFG Boss and get picked up by Big Boss ( people might hate you for this )
Vex ( if I have a group running ) and I will pick you up
Or keep an eye on in zone for people asking for members