Yes, you can get an adaptor to fill the cylinder off the rifle.

The brass cup (as I call it) fits over the T-bar on the cylinder and the cup is then rotated so that the T-bar locks it on (the T-bar straddles the T slot in the brass cup). As your using a pump, while you're pumping check the pump body every now & then for warmth. If the pump body is warm, let it rest until cool before continuing to pump. Basically, the warmth creates moisture that the pump might pump into the cylinder. Fill to about 170-190 BAR (you'll have to test your rifle's power to determine which fill pressure it prefer's.... 170, 180, 190). Once desired pressure has been achieved, open the bleed valve to release pressure in the hose then detach the brass cup from the cylinder.