I found a solution - as always when you know it, it was not that difficult.
Before adding it to trunk I'd ask you to test it. Please copy the attached TADrawerCanvas unit over the original one (it is in (lazarus)\components\tachart); you may want to make a copy of the original one in case you want to switch back again. Recompile the TAChart package. That should be all.
In order to copy a chart to the clipboard as a metafile use the same code as for saving to file, but leave the file name empty:
procedure TForm1.btnCopyToClipboardClick(Sender: TObject);
begin
with Chart1 do
Draw(TWindowsMetafileDrawer.Create(''), Rect(0, 0, Width, Height));
// Setting the file name to an empty string results in copying the chart to
// the clipboard.
end;
Not really straightforward, but I cannot add a CopyToClipboardMetafile method (like CopyToClipboardBitmap) to TChart because the wmf stuff is in a separate package (for good reasons...)
Note that this code runs only under Windows.