Ghostly Warder is a Major Virtue so I'd be inclined to interpret liberally. Especially since I could find little discussion on the Atlas Games email list, implying that players see the virtue as weak or not interesting enough.
Since, as you say, the Warder has Magic Might, you could rule that anything with Magic Might counts as a "non-hermetic Wizard" (Aegis of the Hearth, p163 ArM5 core) able to take part in the ritual.
Additionally, the example Ghostly Warder has the Kinesis power (p193, ArM5 core) allowing "her to move one object until she puts it down". Seems simple enough to be given a token, carry it across the ritual boundary. Indeed, there's no duration limit specified on Kinesis, so she could constantly carry the token inside the Aegis (and then not be able to interact with any other physical object).
Of course if you rule the Warder is not qualified to be a "non-hermetic Wizard", if they put the token down then they are inside the Aegis without a token. There are a variety of consequences to this. I would recommend reading callen's post "A Guide to Aegis of the Hearth" in the Atlas Games email archive for some of the options to be discussed.
These possibilities could easily generate interesting storylines (e.g. visiting another Covenant, taking something critical to the PC from a visitor to PCs covenant, etc). If the troupe thought the extra mechanical interpretation had enough story/fun potential, leaving open the possibility of Aegis consequences for the Warder could be a great direction to take the Virtue.