In fact, you can do:
(v0.7) pkg> activate NewEnv
[ Info: new environment will be placed at /Users/kev/julia/NewEnv
julia> using Pkg
julia> for p in readlines(expanduser("~/.julia/v0.6/REQUIRE")
Pkg.add(p)
end
And it will install all the packages in your v0.6 REQUIRE file and build a manifest.
Edit: note that the ] activate NewEnv isn’t strictly necessary, if you just leave it in the base v0.7 environment it’ll work too