I'm sorry to interrupt, but could I make a comment?
I'm sorry to cut in, but if I could add something to what you were saying...
Excuse me, but could I say something to that?
ご質問ありがとうございます。
① "I'm sorry to interrupt,"=「遮ってすみません、」
"but could I make a comment?"=「でもコメントをしても良いでしょうか。」
② "I'm sorry to cut in,"=「遮ってすみません、」
"but if I could add something to what you were saying...."=「でも、もし今おっしゃっていたことに付け加えて良いのでしたら...」
③ "Excuse me, but could I say something to that?"=「すみません、でもそれについて発言しても良いでしょうか。」
ご参考に。