Pfsense ipsec VPN client to Cisco

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People say there are no stupid questions but this may just be one…

Current situation:
Office is set up with Cisco router that accepts incoming Cisco VPN clients (old style, ipsec). Users use Cisco Windows VPN client to connect.

What I would like:
Instead of Windows VPN client, I'd like to set up pfsense to connect to the office VPN server without modifications to Cisco router. Basically, it would have to look on the server side like incoming connection is from Windows client.

All tutorials I've seen so far talk about site-to-site connection, where configuration on Cisco server side is modified to know about connecting pfsense. I don't have access to Cisco router, and people who do are not willing to go with site-to-site configuration (understandable). I would just like to avoid installing desktop client if possible and pass VPN responsibility to pfsense.

So, is this possible? If it is, any pointers to configuration?