I view this situation generically as akin to talking to the "actives" in a sequence where there's not enough time to tell everyone what to do in the call (as opposed to the walk-through).
In this case, the Allemande folks are moving first and therefore "active." I've used a call of "Gents Allemande Left once and a half, hold on, Ladies join your Partner for a Star Promenade.." (or the reverse) but it's more wordy than the "pick up your _____" or "pick 'em up" variant.
In my teaching I try to stress to the "picked up" folks that they are active participants and it's important to stay aware, facing the right direction and ready to merge up to speed into the promenade (akin to cars on an on-ramp) - so all arrive on time for the next bit.