Straightforward 39 bytes (37 + 2 flags) solution :

#!perl -pl
/\d+\+/;$-+=rand$&for 1..$_;$_+=$'+$-
[download]

More complex 35 bytes solution :

#!perl -pl
s/d/q(+~~rand($')+d)x$`/e;$_=eval
[download]

Due to the use of $', they can’t easily be ran from the command-line. Just store them in a file.