It's doable, at least with my GF Soundwave.
Instead of having soundwave's legs straight you position them both one click outwards at the hip and then bend the knees one click inward. The pegs on the knees should now line up with the cockpit piece and both the feet should be pressed up flush against the nosecone.
Personally I prefer to mistransform and keep the legs straight with the pegs not clicking into the cockpit and the toes tapping into the nosecone. It makes him look less 'holey'.