I have installed widshields before using the soapy string trick. Don't know if this will work for you, but link is below. Trick is to put the gasket around the glass, then put a soapy string in the body channel groove of the gasket, have someone gently push on the glass as you pull the string around the gasket from the inside. As you pull the string, the lip of the gasket will be pulled over the body flange. Have a piece of plastic available to help.

Hope this works for you..

Kurt

Soapy string trick