If he had more faith in Childermass' ability to remain conscious, he might try the portal. As it is, he worries if he lets go that'll be the end of his focus.

So Syrlya moves him over, as quickly but carefully as he can, to heavy him onto Lambert's back--probably hanging limply. Syrlya hauls himself up right behind Childermass and waves a hand to put them all under stealth before putting a firm hand on his arm and torso as he sits back to try and anchor his weight.

"All right, go."