Quick modification for multiple values - not the most concise, but this is being compiled pre-upload...

rem-fallback.less

@main-font-size: 16px;

.x-rem (@property, @value) {
  // This is a workaround, inspired by https://github.com/borodean/less-properties
  @px-fallback: @value * @main-font-size;
  -: ~`(function () { return ';@{property}: @{px-fallback}'; }())`;
  -: ~`(function () { return ';@{property}: @{value}rem'; }())`;
}
.x-rem (@property, @v1, @v2) {
  @px-v1: @v1 * @main-font-size;
  @px-v2: @v2 * @main-font-size;
  -: ~`(function () { return ';@{property}: @{px-v1} @{px-v2}'; }())`;
  -: ~`(function () { return ';@{property}: @{v1}rem @{v2}rem'; }())`;
}
.x-rem (@property, @v1, @v2, @v3) {
  @px-v1: @v1 * @main-font-size;
  @px-v2: @v2 * @main-font-size;
  @px-v3: @v3 * @main-font-size;
  -: ~`(function () { return ';@{property}: @{px-v1} @{px-v2} @{px-v3}'; }())`;
  -: ~`(function () { return ';@{property}: @{v1}rem @{v2}rem @{v3}rem'; }())`;
}
.x-rem (@property, @v1, @v2, @v3, @v4) {
  @px-v1: @v1 * @main-font-size;
  @px-v2: @v2 * @main-font-size;
  @px-v3: @v3 * @main-font-size;
  @px-v4: @v4 * @main-font-size;
  -: ~`(function () { return ';@{property}: @{px-v1} @{px-v2} @{px-v3} @{px-v4}'; }())`;
  -: ~`(function () { return ';@{property}: @{v1}rem @{v2}rem @{v3}rem @{v4}rem'; }())`;
}

.some-class {
  .x-rem(font-size, 1.4);
  .x-rem(margin, 1.4, 0, 2, 2.3);
}

rem-fallback.scss

$main-font-size: 16px;

@mixin x-rem ($property, $value) {
  #{$property}: $value * $main-font-size;
  #{$property}: #{$value}rem;
}

.some-class {
    @include x-rem(font-size, 1.4);
}

Thank you! The best example of implementation, from what I have seen previously