How to send traffic as different subnet.

[lasmith]

I'm not sure how to phrase this question properly, but here goes.

I have an IPSEC tunnel that requires traffic comes in on 10.10.10.x
My main LAN is using 10.10.20.x

I would like to setup a pfsense box to nat or alias all 10.10.20.x traffic to 10.10.10.x

Is this possible? And if so what would I have to configure to make this happen.