Bicycle Mechanics - Converting from twist shift to rapid fire

I have large hands and really would prefer a rapid fire style shifter to the current twist grip on my tern Link D7i. I want more options for grips.

It currently has the Shimano Nexus 7 speed twist for my Nexus 7. I haven't found anything that is clear cut if I can do this. I have seen some mention using the alfine 8 speed shifter but only using 7 selections instead of 8. Is this possible without messing up the Nexus 7?

I am not familiar with bicycles as a newb but capable of doing any work needed once I get some guidance.

Errrrmmmmm I'm doing something similar, so I can tell you what I know you need to look into.. first is pull ratios, make sure both shifters use the same one(that's the big one), other thing is you'll need to set the rear derailer limit, so even if you do hit the 8th click on the rapid fire, the derailer won't move over and launch the chain off.

The pull ratio was something I was thinking about. Also since my bike is an internal gear hub Nexus 7 I don't have a rear derailer to worry about.

Duh I should know that.. I have a nexus rear coaster wheelset. So just make sure about the pull ratio and in my inexperienced mind, you should be good.

See what the distributors that your local bike shop uses , has to draw from..

it is possible to make up a scale and a cable jig to see how far it is
between the gear selections on an IGH.

Others have done this, then made their own travel agent like dual diameter pulleys
[being home machinists]