How can prayer ever be illicit?? I follow the Mass in my missal, always have, so is the reading and contemplation of the words any different than whispering them?? If so, the missal is an occasion for sin!!! I don't think so.
There is a reason the Church forbade hand missals until the 19th century (the Roman Canon, which was said silently by the priest until 1967 was not allowed to be printed for a good while)
How can prayer to God be illicit? When it is a prayer that calls for an ordained priest*. To meditate on the Canon and Sacrifice and even to unite with it in the priesthood of the laity is not only licit but what you should be doing,
The problem is when people blur the lines between the ordained priest and the laity, think they somehow have the power to consecrate, etc. The Church forbids the laity to say the Canon with the priest, including the per ipsum (Through Him, with Him, etc) for this reason. But the law is intended against the congregation usurping the parts of the priest. I do not think mouthing the words, provided one knows they aren't "concelebrating" is what is intended when these parts are forbidden to the laity.
*The prayer for absolution "ego te absolvo a peccata tuis in nomine patris et filii et spiritus sancti" is a good example. These words effect absolution when said by a priest. If I were to say them over a penitent it would only effect my automatic excommunication from the Church for impersonating a priest