I understand what you mean, and I would be happy to fulfil your request, however lynxchan only provides me with the option to lock, pin or make a thread cyclical. The board page limit is 25, however, so I think it will not have been pushed off the edge of board a year from now.
There isn't an option to sticky this thread at the bottom of this page, basically.
Sorry that I can't do what I think you want.
I'm a big fan of Haibane Renmei. Comfy picture!