Mounting only by the camera body can work, but with a heavy telephoto zoom the setup will be front-heavy and less balanced. If your head is very solid it may hold, but it’s not the best solution.

A better approach is to support the lens itself. Two options mentioned were:

• a lens support device (such as the Manfrotto 293 style of support), which cradles the lens and can be adjusted for different lengths
• a gimbal-based setup with an adapter plate, which is especially useful for heavy telephoto lenses

In general, a tripod collar is the ideal solution because it balances the lens/camera combination around its center of gravity. If your lens does not have one, a lens support is the most practical alternative. It should be easier to find and less specialized than trying to improvise a mount from the camera body alone.

So: yes, body-only mounting is possible, but for stability and balance, use a lens support or collar-style solution whenever you can.