What about 30 metres or 10 MHz? That's easy if they have a dipole with tuned feeders and a good antenna coupler. Otherwise it requires modifying an existing antenna or putting up a new one dedicated for the band.
Is this worthwhile? At the current phase of the solar cycle there are times when 30 metres is open but 40 metres isn't. If you're into single hop communication of around 1000 to 1500km there are times when that is too short for 20 metres but signals are weak on 40 metres.
Not into contesting? 30 metres is a quite haven for you since contests are not run there. Then there are the DX prospects of 30 metres, especially if you are into digital modes. 30 metres can come into its own in the late morning when 40 metres fades out but before 20 metres comes in. And vice versa in the afternoon.
As for the antennas people use, a beam is out of the question for most. But there is a big choice of less visible wire antennas. These include dipoles, verticals and even beams. The usual rules apply. If you want DX go for a low angle radiator. Suitable antennas include a high dipole (at least 1/2 wavelength off the ground) or a vertical with good radials over a conductive earth.
Here are some ideas for 10 MHz antennas that other hams have found effective:
* K7EA 30m ground plane
* N2RIT 30/40m black box vertical
* I2NDT coaxial cable dipole for 30m
* ON8IM 30m bobtail
* M0MCX 30m rotatable delta loop
* N6JV 30m beam
* Eham discussion thread on 30m antennas