Hello Julian,
I don't see why you cannot add this control directly the the page. You could also try adding the asp:LinkButton control directly on the page layout and nest the OnClick handler within scripts tags:
<asp:LinkButton runat="server" ID="lnkBtn" OnClick="OnClick" />
<script runat="server">
protected void OnClick (object sender, EventArgs e)
{
// Here goes your custom code
}
</script>
Also, please ensure you are inheriting from the Kentico CMS controls - CMSAbstractWebPart -
devnet.kentico.com/docs/devguide/developing_web_parts.htmBest Regards,
Edward Hillard