We give a construction of impurity operators in the 'algebraic analysis' picture of RSOS models. Physically, these operators are half-infinite insertions of certain fusion-RSOS Boltzmann weights. They are the face analogue of insertions of higher-spin lines in vertex models. Mathematically, they are given in terms of intertwiners of Uq (s-fraktur sign and l-fraktur sign2) modules. We present a detailed perturbation theory check of the conjectural correspondence between the physical and mathematical constructions for a particular simple example.