SASS: rempx mixin. Get pixel-based and rem-based "property: value(s)" set. concat-list(), strip-unit(), rem-calc() functions and Sass ver.3.2.0~ are required.

gistfile1.sass

@mixin rempx($property, $values...) {
  $values: concat-list($values);
  $max: length($values);
  $pxValues: '';
  $remValues: '';

  @for $i from 1 through $max {
    $value: nth($values, $i);
    @if $value == auto {
      $pxValues: #{$pxValues + $value};
      $remValues: #{$remValues + $value};
    }
    @else {
      $unit: unit($value);
      @if $value == 0 or $unit == "%" {
        $pxValues: #{$pxValues + $value};
        $remValues: #{$remValues + $value};
      }
      @else {
        $value: strip-unit($value);
        $pxValues: #{$pxValues + $value}px;
        $remValues: #{$remValues + rem-calc($value)};
      }
    }

    @if $i < $max {
      $pxValues: #{$pxValues + " "};
      $remValues: #{$remValues + " "};
    }
  }

  #{$property}: $pxValues;
  #{$property}: $remValues;
}

Usage example:
@include rempx(margin, 16px, 32px, 32px, 16px);
then you'll get:
margin: 16px 32px 32px 16px;
margin: 1rem 2rem 2rem 1rem;
NOTE:

• Writing "@include rempx(margin, 16 32 32 16);" gets same result.
• This mixin can also treat "%" and "auto". e.g. @include rempx(margin, 15, auto, 20%);

SHOW ME HOW TO DO THIS PLE

• concat-list() function: https://gist.github.com/githiro/fc2250b079475e3cc7fa
• rem-calc() and strip-unit() function: https://github.com/zurb/foundation/blob/master/scss/foundation/_functions.scss

This function is based on the assumption of using Foundation framework(http://foundation.zurb.com).