$web = get-spweb "http://www.questionstackexchange.fr/subsite";
$list = $web.lists["MyLittleList"];
$files = $list.rootfolder.files;

$form = $list.RootFolder.files | ?{$_.url -match "dispform.aspx"};
$form.delete();
$list.update();

$dispformurl = $list.RootFolder.ServerRelativeUrl + "/Dispform.aspx";
$dispform = $files.add($dispformurl, [Microsoft.SharePoint.SPTemplateFileType]::FormPage);
$wpm = $dispform.GetLimitedWebPartManager([System.Web.UI.WebControls.WebParts.PersonalizationScope]::Shared);
$lfw = new-object ([Microsoft.SharePoint.WebPartPages.ListFormwebpart]);
$lfw2 = new-object ([Microsoft.SharePoint.WebPartPages.ListViewWebPart]);
$ilist = [Microsoft.SharePoint.WebPartPages.IListWebPart]($lfw);
$ilist2 = [Microsoft.SharePoint.WebPartPages.IListWebPart]($lfw2);
$ilist.ListId = $list.id;
$ilist2.ListId = "B4A7D0D0-221D-492C-B6E6-A5D758EDD3F2";
$ilist.PageType = [Microsoft.SharePoint.PAGETYPE]::PAGE_DISPLAYFORM;
$ilist2.PageType = [Microsoft.SharePoint.PAGETYPE]::PAGE_DISPLAYFORM;
$wpm.AddWebPart($lfw, "Main", 1) ;
$wpm.AddWebPart($lfw2, "Header", 1) ;
$list.DefaultDisplayFormUrl = $dispformurl;
$list.update();