It looks like 'guix environment' does not handles derivations-as-files.
I don't know if it's a bug in the package or 'guix environment':

$ ls -l /gnu/store/i1139n4ab0fn9v4bwkvqzp6sw3w66mqr-python-waf-1.9.5
-r-xr-xr-x 2 root root 99280 Jan  1  1970 /gnu/store/i1139n4ab0fn9v4bwkvqzp6sw3w66mqr-python-waf-1.9.5

$ ./pre-inst-env guix environment mpv
The following derivation will be built:
   /gnu/store/b5ph69m9z0qgwkf1w1p39r3wyab6x4hi-profile.drv
Backtrace:
In ice-9/boot-9.scm:
 160: 14 [catch #t #<catch-closure 8cad00> ...]
In unknown file:
   ?: 13 [apply-smob/1 #<catch-closure 8cad00>]
In ice-9/boot-9.scm:
  66: 12 [call-with-prompt prompt0 ...]
In ice-9/eval.scm:
 432: 11 [eval # #]
In ice-9/boot-9.scm:
2404: 10 [save-module-excursion #<procedure 8ea7c0 at ice-9/boot-9.scm:4051:3 ()>]
4056: 9 [#<procedure 8ea7c0 at ice-9/boot-9.scm:4051:3 ()>]
1727: 8 [%start-stack load-stack #<procedure 8fcba0 at ice-9/boot-9.scm:4047:10 ()>]
1732: 7 [#<procedure 8fd6f0 ()>]
In unknown file:
   ?: 6 [primitive-load "/gnu/store/yax60hx75hyarsfpraplhhfhkaqs30ia-profile-builder"]
In ./guix/build/profiles.scm:
 133: 5 [build-profile "/gnu/store/dd9fznm75rdjkdhb4zqz67lvr8d1ya5d-profile" # ...]
In ./guix/build/union.scm:
 136: 4 [union-of-directories "/gnu/store/dd9fznm75rdjkdhb4zqz67lvr8d1ya5d-profile" ...]
In srfi/srfi-1.scm:
 613: 3 [for-each #<procedure a86c80 at ./guix/build/union.scm:136:16 (dir)> #]
In ./guix/build/union.scm:
 138: 2 [#<procedure a86c80 at ./guix/build/union.scm:136:16 (dir)> "/gnu/store/i1139n4ab0fn9v4bwkvqzp6sw3w66mqr-python-waf-1.9.5"]
  37: 1 [files-in-directory "/gnu/store/i1139n4ab0fn9v4bwkvqzp6sw3w66mqr-python-waf-1.9.5"]
In unknown file:
   ?: 0 [opendir "/gnu/store/i1139n4ab0fn9v4bwkvqzp6sw3w66mqr-python-waf-1.9.5"]

ERROR: In procedure opendir:
ERROR: In procedure opendir: Not a directory
builder for `/gnu/store/b5ph69m9z0qgwkf1w1p39r3wyab6x4hi-profile.drv' failed with exit code 1
guix environment: error: build failed: build of `/gnu/store/b5ph69m9z0qgwkf1w1p39r3wyab6x4hi-profile.drv' failed

-- 

  Sergei