The Flight Connection area is just towards the end of those awful long corridors in T4 that you use when arriving into T4 and before you get to the UK Border. Just before passports there is a sharp turn, clearly signposted, that takes you into T4 Flight Connections, and on to the T5 bus. No security there, it's all at T5. So this route entirely bypasses T4 departures.

Now you could in theory ask to go "shopping" in T4 upon arrival at T4 Flight Conenctions, then you would go through an extra security check at T4, then after "shopping" you have to reverse your way out again via Flight Connections. But at that point you may as well go landside anyway, and you wouldn't do it in 45 minutes.