Later on, Shunpei admits to Fumi that only fingers were used and the president never got around to using any toys.
I don't think the president used his fingers because, in this page ( http://www.mangago.me/read-manga/elektel_delusion/mf/v04/c020/31/), Shunpei thought he succeeded to escape the fingers and, in this one ( http://www.mangago.me/read-manga/elektel_delusion/mf/v04/c021/15/), he said the only interest of Satonaka was to interfere in his relationship with Fumi and giving him fingers.
And later, when Shunpei explained what happened to Fumi, Shunpei said about Satonaka "Then, if he didn't use his fingers there, he wouldn't have seen it (the mole)".
Here: http://www.mangago.me/read-manga/elektel_delusion/mf/c021.5/10/
I think that Satonaka "just" gazed at Shunpei's arse.
Maybe I'm confused, but all of your quotes and references point to his fingers being used IMO. The quote "Then, if he didn't use his fingers there, he wouldn't have seen it (the mole)." leads to the conclusion that, because Satonaka did know about the mole he had therefore used his fingers.
no he didnt... go again through the pages pointed out by @alohomori and its clear that he just gazed at the bare butt
You got me... the last thing I'm in the mood to deal with is some pissed off fujoshi over whether or not a fictional character got a finger stuck in his boy-pussy. Believe what ever gets your little fan-girl heart fluttering. It matters little to me. I read and interpreted it differently, that's why I used "IMO" (IN MY OPINION).
So how much did president do to shunpei, I'm guessing it was a finger but nothing else, but maybe I'm wrong and he did it with the vibrator.