basically no! dash needs to come out becasue as i say, the knee bar runs in front of the heaterbox so ytou cant pull it forward. plus if you have aircon, the pipes for it pass thru the bulkhead so these will probably need to be disconnected.
you might if you're lucky be able to pull the heaterbox back enough with the A/C pipes still attached, but it depends on the shape of the pipes at the bulkhead. i.e. if they stick straight out you can pull it out, if they angle 90degrees right at the bulkhead obv not gonna move back very far.