I just found this one k-chan news episode where Shige was the guest and one listener said she was very surprised when in some interview Shige said he'd kissed Koyama before. Apparently they asked him about kissing scenes in dramas and such and that's when he said it. They discussed it on the radio a bit but I wanted to know if anyone knows which interview that was.
Edit: I found it! Here's that part:
S: No, no! I don't want other members see my kissing face at my wedding! (laugh)
T: But Kei-chan, you've/we've seen Shige kissing before, right?
K: Eh? We did? (laugh)
S: Well, me and Koyama actually kissed before (laugh)
They also discussed it in more detail on the radio. I have translated the whole segment and added the recording here: Kちゃん NEWS 2013.02.20
But I have to warn you that you may never see this band in the same way again. Also just letting you know that the whole kissing incident very much involved Tegoshi.