Choose the Automation template. Click the Library button in the toolbar to get a list of available instruments. Find the Allocations instrument in the Library and drag it to the instruments list on the left side of the trace document window. You could also reverse this by choosing the Allocations template and dragging the Automation instrument from the Library.
After you add the second instrument from the Library, choose File > Save As Template to save your trace as a template. When you profile your app in Instruments, your template will appear in the list of available templates in the User section. Saving as a template keeps you from having to add a second instrument to the trace every time you profile your app.