Uh, this is a difficult task and hardly achievable in case of multiple samples and limited funding. Genotyping by Sequencing or Metabarcoding-like approaches would solve this task, but are not suitable for numerous samples. I would rather try to work on the hair sampling device... or try the analyses with single hairs or skin scales (latter ones are usually enough to allow for PCR amplification, single hairs might be difficult for voles ;-) Alternatively, adapt your sampling design, e.g., by placing several traps at the sample location, so that the chance is low to have more that one individual at one trap ("digital sampling"). Good luck!