// this finds the name of the group the selected object belongs to
string $p[] = `listRelatives -fullPath` ;
$p = stringToStringArray( $p[0], "|") ;
$gOriginal = $p[0] ;

// duplicate the selected object and move it to root
duplicate -rr -n refOrig ;
parent -w refOrig ;

// move the object to the root of GROUP the selected object belongs to
parent refOrig $gOriginal ;

// you may or may not want this, I had a subgroup inside the group
// and wanted the duplicated object to be the first object in it
reorder -relative -1 refOrig ;

// create a new reference plane at 0, 0, 0. 100 units wide/deep
nurbsPlane -p 0 0 0 -ax 0 1 0 -w 100 -lr 1 -d 1 -u 1 -v 1 -ch 1 -n refPlan ;

// you may want to change this, I wanted the corner to be at 0, 0
// so X and Y goes -50. for my purpose I also moved it up 75 units.
setAttr "refPlan.translateX" -50 ;
setAttr "refPlan.translateZ" -50 ;
setAttr "refPlan.translateY" 75 ;

// select 3 vertices on the original object
select -r refOrig.cv[0][0] ;
select -tgl refOrig.cv[0][1] ;
select -tgl refOrig.cv[1][1] ;

// select 3 vertices on the reference plane
select -tgl refPlan.cv[1][0] ;
select -tgl refPlan.cv[1][1] ;
select -tgl refPlan.cv[0][1] ;