Check ebay for a cheap way to hold up ( I would not use them, but may work), some folks offer a bag of "pins" that can be shoved into the liner and board. Look up headliners. I have no idea how well this works. I owned an 89 Lesabre and believe or not replacing the liner is not difficult on it. If interested I can look up the place I bough mine(on the internet) and you can give it a try. Only took me 2 hours to do and looked great. The site has online instructions on an 89 Buick and once you look at it you will see how easy it is. Far easier than the other vehicles I have done.
Here, give it a check -
http://www.wlsheadliners.com/tutorials/lesabre/