Need Creative Suggestion: binder from Shower Stall to Wallboard

As you know...when you work on an old house, you need a lot of creativity and non-standard solutions.
I put in a fiberglass showerstall in the bathroom in a converted sideporch BUT one side sticks out of the wall about eight inches so I glued greenboard to that side....leaving the gypsum edge exposed. Temporarily, I've put black duct tape on as a binder. What can I use permanently? There is a curved part at the top of the shower so a straight metal U shaped channel will not do. This stumped the local hardware guys!
Thanks for your help.
Dean in Cincy snipped-for-privacy@aol.com
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Deano wrote:

Extend out your wall and finish normally?
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