I'm a support main in a pretty low in ELO. I don't play with other ADCs besides my brother or another great friend of mine.
While watching some of the LCS games, I noticed that the supports are usually way behind in experience points than anyone else on the team.
How can I give my AD carry more experience in the laning phase while making sure they still do well?
I don't want to stay and soak up the experience, or roam and leave my ADC to start losing.
You cannot. Well, you can but it's risky, risky enough that it comes down to who is your ADC.
As you know by now (hence the question), two or more champions near a minion/champion death results in less experience gain. That is why a common tactic (not necessarly only in LCS) is to leave the ADC alone, in order for him to obtain more experience.
How can I give my AD carry more XP in the laning phase and make sure they still do well instead of staying and soaking it up, or roaming and they start losing?
Well, for one there's Zilean's passive like @Dragonrage mentioned in the comments, but I suspect you want a more definite answer than "play x champion".
What you need to ensure is that your ADC will still be able to farm without you, and that he won't die without you. In other words, you need to ensure that:
There's also another situation which is jungling, depending on who your botlane is, you can sometimes go into the jungle and take a camp or two to gain some experience if you're zoned in lane. In this case both you and the adc would take a camp and get a small experience boost instead of gaining no exp at all. However this depends heavily on your own jungler's routes and what he's trying to do at that momment.
Finally the most important thing is: You are being useful. There is no point in roaming to let your adc get level advantage if you're getting even further behind. Let's say you roam and your ADC is level 6. Their botlane is level 5 and you're level 4. They are ahead because they will have their ultimates on a 2v1 situation, or on a 2v2 situation before you have your own ultimate ability. As such you should only do those roams if you're being productive (Taking Dragon, Ganking Lanes, Peeling on jungle skirmishes)
