Is there a way to trigger iPad sleep using gestures?
You can enable the assistive touch panel. From this panel you can put the iPad to sleep with the touch screen.

To enable assistive touch:


Tap Settings
In Settings Submenu tap General
Scroll down the General submenu to find Accessibility.
Tap Accessibility.
In the Accessibility submenu tap AssistiveTouch
Trigger Assistive Touch into ON state


This menu (which can be minimized into every corner on your screen) allows you to do several actions using the touch screen, including sleeping the iOS device.