I'd rotate the graphics before-hand and restore afterwards:
#!/usr/bin/perl
use PDF::API2;
my $img1="../first.gif";
my $pdffile="../sample.pdf";
my $pdf = PDF::API2->new( -file => "$pdffile" );
my $page1 = $pdf->page;
$page1->mediabox('A4');
my $photo1 = $page1->gfx;
my $photo_file1 = $pdf->image_gif($img1);
$photo1->save;
$photo1->transform(
-rotate => 45,
-translate => [my $_x = 100, my $_y = 50],
);
$photo1->image( $photo_file1,50,360,510,250);
$photo1->restore;
$pdf->saveas($pdffile);
$pdf->end();
There's likely to also be some translation involved depending on what corner you want to pivot from.