You know the day is good when you beat one of design problems.
GL11.glEnable(GL11.GL_STENCIL_TEST); // Turn on da test
GL11.glClear(GL11.GL_STENCIL_BUFFER_BIT); // Flush old data
GL11.glStencilMask(0xFF); // Writing = ON
GL11.glStencilFunc(GL11.GL_ALWAYS, 1, 0xFF); // Always "add" to frame
GL11.glStencilOp(GL11.GL_KEEP, GL11.GL_KEEP, GL11.GL_REPLACE); // Replace on success
//Anything rendered here becomes "cut" frame.
GL11.glStencilMask(0x00); // Writing = OFF
GL11.glStencilFunc(GL11.GL_NOTEQUAL, 0, 0xFF); // Anything that wasn't defined above will not be rendered.
//Anything rendered here will be cut if goes beyond frame defined before.
GL11.glDisable(GL11.GL_STENCIL_TEST); // Turn this shit off!
EDIT: Edited code to more universal.