A endfed vertical for 40m is around 67'

No it is not. A 1/4 wave vertical for 40M is around 33'. If mounted at
ground level it requires an extensive ground radial system to get good results.
If you are talking a 1/2 wave vertical better to feed it in the center.
An inverted "L" with 33' vertical and 33' horizontal is around 67'. Still
requires a good ground.

Could a coil be placed in the
center of the endfed wire to shorten it to say 40'

Yes, but you need to remember the radial requirements, and if you start
sticking coils in the antenna, then the matching starts being a problem.
This would make it
easier for my portable QRP
For QRP and portable operation 40m-10m, a 50'-100' inverted vee fed with
300-450 ohm balanced line and a tuner. Get the apex up as high as possible.
You can not beat this for multi-band portable operation.
73 Gary N4AST