Answer: Bot Fly larvae
As Bill mentions in his comment, he tried to rear two of these larval flies to adults but they did not enter the pupation stage (the next step of development prior to the emergence of the adult). If we could have examined the adult fly, identification to the species level would have been more straight-forward. However, we can say that based on the features of the larvae, these are most likely Cuterebra spp.
In nature, these larva drop off the rodent host and pupate in the ground. They then emerge as adults.
Thank you for all of the comments on this interesting case.