There is no way to blend multiple templates. The recommended way to go about this is to register multiple views of the same fingerprint under one user ID. Identification algorithm uses all available fingerprints to produce more accurate similarity score. Negative impact of this is lower identification performance, because all views of the same fingerprint are processed by identification algorithm. The negative impact is observable only if large fraction of registered users have multiple views of the same fingerprint or if you use such a user record as probe (in IEngine_FindUser() method).
For registration we recommend to use just one view of same fingerprint, which is chosen as best quality fingerprint template from three candidates (add three fingerprint images into user record, get the candidate with highest quality and remove the rest).