HaveFun

$text = 'Шла саша по шоссе и сосала сушку';

$arWords = explode(' ',$text);
function implodeAndNest($arWords,$firstElement = null){
  $arResult = array();
  foreach($arWords as $wordNum => $word){
    if($wordNum == 0){
      $result = array(implode(' ',array_slice($arWords,$wordNum)));
    }else{
      $result = array(implode(' ',array_slice($arWords,0,$wordNum)),implode(' ',array_slice($arWords,$wordNum)));
    }
    if(isset($firstElement))
      $result = array_merge(array($firstElement),$result);
    $arResult[] = $result;
  }
  return $arResult;
}

$arResult = array();
foreach($arWords as $wordNum => $word){
  if($wordNum == 0){
    $arResult = implodeAndNest(array_slice($arWords,$wordNum));
  }else{
    $arResult = array_merge($arResult,array_values(implodeAndNest(array_slice($arWords,$wordNum),implode(' ',array_slice($arWords,0,$wordNum)))));
  }
}

// удаляем лишние результаты
$arResult = array_values(array_map("unserialize", array_unique(array_map("serialize", $arResult))));

echo '<pre>';
print_r($arResult);
echo '</pre>';

$text = 'давайте выражаться культурно';

$arWords = explode(' ',$text);

function implodeAndNest($arWords){
  $arResult = array();
  foreach($arWords as $wordNum => $word){
    if($wordNum == 0){
      $arResult[] = implode(' ',array_slice($arWords,$wordNum));
    }else{
      $arResult[] = array(implode(' ',array_slice($arWords,0,$wordNum)) => implode(' ',array_slice($arWords,$wordNum)));
    }
  }
  return $arResult;
}

$arResult = array();
foreach($arWords as $wordNum => $word){
  if($wordNum == 0){
    $arResult[] = implodeAndNest(array_slice($arWords,$wordNum));
  }else{
    $arResult[] = array(implode(' ',array_slice($arWords,0,$wordNum)) => implodeAndNest(array_slice($arWords,$wordNum)));
  }
}

echo '<pre>';
print_r($arResult);
echo '</pre>';