Seal hole in in-wall toilet tank

Half a year back our contractor installed in-wall toto toilet with the tank inside the wall. It turned out while drilling hole for something else he went too far and made a tiny hole in the tank's bottom right corner. Now it is slowly leaking. He accepted the fault and wants to fix it by his expense, but it requires replacing multiple wall tiles and etc . We are leaving it as the last option, but we are looking for other ways to avoid breaking the wall. Luckily my wife is able to squeeze her hand through the control panel opening and inside the tank, and she can feel the hole, it feels like a a tiny knob. So, she can put some glue on her finger and apply it directly to the hole, she also can do some sanding before that, and maybe even apply a patch if needed(not sure it will be ideal though - space is tight, all operations will be done blindly). The complexity is that as far as I know the tank is made from polyethylene and most of glues don't work well with it, and welding is out of question due to the limited space and inability to watch the process. Question - do you think fixing hole in polyethylene tank is possible under the mentioned conditions? If yes, what glue can you recommend?