You can insert a button (via an <input> element) that will link to specified URL without manually inserting the HTML by creating a custom widget, below are some steps outlining the process of creating and using a custom widget:

• Go to Tools > Options > Widgets
• Click the Create a new item toolbar button
• In the widget editor window set the Caption to Button
• Enable the Use different Html for design time and output option
• In the Content editor switch to XHTML view and paste in the following:
  

  <input type="button" onclick="location.href = '%%href%%';" value="%%value%%" />
  

• In the Design Time Content editor switch to XHTML view and paste in the following:
  

  <div>
      <h4>Button</h4>
      <p>href: %%href:layout=inline%%</p>
      <p>value: %%value:layout=inline%%</p>
  </div>
  

You can now insert buttons via the Button entry on the Widget menu (available on the Content Authoring ribbon tab).