I doubt that this is an acceptable solution, but the only solution I know to
smoothing rippled paper is to dampen the paper and stretch is on a board,
applying brown paper tape to the edges and stapling with a staple gun if the
paper is heavy. This means sacrificing an inch or more of the margins of
the artwork, which you may not be able to sacrifice, and the possibility of
damaging the drawing by getting it wet.
I did this technique years ago as an art student, so there may be more up to
date methods for stretching paper. Our GNSI chapter, (Great Lakes) recently
visited a restorers studio in Chicago. It is amazing what can be done to
damaged artwork to restore it. Perhaps a call to a restorer/conservationist
could answer your questions definitely about whether ink drawings can
tolerate rewetting, and whether stretching or pressing will give you the
results you want.