This is probably the opposite problem most authors have when publishing. I don't want the Kindle version's page count changing when I publish the CreateSpace paperback. Normally, the page count rises to match the paperback, but it won't with my book, because the print version has fewer pages.
My Kindle ebook has 180 pages, but the 9x6-sized paperback will only have 140. If I publish the paperback, I don't want the Kindle version to have the page count reduced to match the print version, as this will make the book appear shorter and less attractive to customers. I'm reluctant to publish the paperback if it means matching the page count to this lower figure. I've read that if the metadata doesn't match that will stop the versions linking, but I don't really want to do that. I want them linked - but I don't want the Kindle version showing the print version's lower page count. If I publish my paperback and the page count is smaller, does the Kindle version automatically match it or does it ignore if it is smaller?
Will I have to reduce the physical size of the paperback/increase margins/font size/line spacing etc. so the page count becomes larger?
With that much of a page-count difference, I'd go for a 5x8" paperback. (That size is actually pretty handsome.) There are also a few other tricks you can use:
1) If you're using Times New Roman 12 in the paperback, try Georgia 12. It's subtly wider and will chew up extra space.
2) You can legitimately add extra page breaks so that chapters or stories always begin on a facing page.
3) You can knock 1/4" off the width of the text you're sending to the PDF image (you do NOT need to fully fill the available printing area, at least not for CreateSpace). 1/4" is not that discernible by the reader; more might be.
4) Lastly, you can very gently bump up the lede ("leading") between consecutive lines of text by a point or two, and see what that does. This, however, will require modifying your paragraph style (I think there's an option to automatically apply it to all paragraphs already in that style, but I haven't done this myself).
You'll want to play with a COPY of your current text file, NOT the original! In fact, I'd save off a copy every time one of these tricks worked, before going on to the next trick.
I've changed the book's dimensions and adjusted the margins to instantly make my book over 200 pages without making it look strange. I'll need to change my cover to new dimensions, but it solves the issue.
The actual listing on the ebook for "page count" is title "Print Length" so if your print book is 140 pages then that is your print length and what should display. This may or may not change once the paperback goes live (it is hit and miss) but if it does then there really is nothing you can do about it.
In the end I doubt it will make much difference. The average reader probably won't base a buying decision on it and it have no effect on Select KENP (if you are in the program)