^^Conventions, hmm... Düsseldorf's Japan Day is in May... that'd be of rather short notice though.
The major London convention is also in May but that usually sells out before they invite music groups though there is another one in July that is Japan themed only. I hope it's not conventions anyway that'd put me off because I hate having to pay a ton of money on tickets and overblown hotel prices when I'm not interested in seeing anything else there.
If you're speaking about the Hyper Japan Festival in July, then they wouldn't be able to do it since there are H!P concerts on those dates...
Looking at the schedule for the summer H!P concerts I think it would be difficult for them to fit it in until after they're finished in September. Unless they squeeze them in between but they'd have to do rehearsals and travel there and so on so its probably not feasible. Also based on how little information we've got, I get the feeling that it's still a little while off, although it's anybody's guess really