\version "2.19.80"

% store the value in an alist
myValues.indent = #'#{ 5\cm #}
myValues.top-margin = #'#{ 5\cm #}
myValues = #`(,@myValues
               (left-margin . #{ 3\cm #}))

% function to calculate the value for the paper block
paperValues =
#(define-scheme-function (vals)(list?)
   (for-each (lambda (p)
               (ly:parser-define! (car p) (primitive-eval (cdr p))))
     vals))
% test
\paper {
  \paperValues #myValues
}

\relative { bes' a c b }