The more distance you can get between the two antennas the less each will be affected by the other. That 'distance' can be vertical instead of horizontal, so raising that discone a couple/few feet above the G5RV isn't a bad idea. That would -lessen- that interaction but it's still going to be there. I doubt if you will notice them 'interacting', it won't be a huge thingy at all.
(Don't touch the center conductor of the discone's feed line to your tongue while transmitting on the G5RV! You definitely WILL notice that.