Hmm there realy is no way to do so internaly within the gui without writing mel. fortunately its rather trivial.
this would create a linear nurbs curve for all motion trails.
{
$selected=ls -dag -et snapshotShape;
for ($obj in $selected){
$pts=(getAttr($obj+".pts"));
$size=size($pts);
$curve=curve -d 1 -p $pts[0] $pts[1] $pts[2] -p $pts[4] $pts[5] $pts[6] -k 0 -k 1;
for($i=8;$i<$size;$i+=4)
curve -os -a -p $pts[$i] $pts[$i+1] $pts[$i+2] $curve ;
}
}
It is possible to amke them update too with a bit of extra work.
Edity fixed code slightly