In order to fit a peptidomimetic compound into a peptide or protein structure, you can load own strutures into SuperMimic (proteins or peptides should be in PDB format; small molecules should be in MDL mol or sd file format, the latter providing several conformers and thus enlarging the search space).
On the other hand, you can utilise the provided structure libraries:

Peptide mimetic libraries

About 100 peptidomimetic compounds have been collected from the literature and have been arranged in sublibraries for alpha-helix-, beta-strand-, gamma-turn-, beta-turn-mimetics. The respective pages under 'Libraries/mimetics' show a picture of each structure, give the library name which is used for it as well as the chemical name and some information about the usage of the substance described in the literature. Each structure is linked to the literature references it was extracted from.
Additionally, the library contains a collection of peptides, consisting of a sequence of a D-amino acid flanked by two L-amino acids, that can be used as beta- or gamma-turn mimetics and some peptidomimetic ligands extracted from the PDB. Other peptide mimetics with known inhibition functions (like thrombin inhibitors), which could not be assigned to one of the previous groups, are classified as drug-like mimetics.
In order to account for the flexibility of the peptide mimetics, each structure is represented by five to 13 low-energy conformers.

Protein libraries

Insertion of peptide mimetics into proteins is realised by chemical syntheses. Such syntheses are mostly practised with small proteins. To allow for rapid and easy identification of candidates for synthesis, the program is linked to a library of small proteins. It contains 10403 chains of PDB structures of at most 100 amino acids length. Alternatively, this large database can be replaced by a set of 2206 chains with less than 90% sequence homology, represented by structures with best resolution.