If you are running pix 6.3 code or hihger on PIX2 then you can employ destination NAT'ing. If you do not want the source hosts to be nat'ed to the pix2 interface address that connects to host2 then you will also need to enable the sysopt proxyarp feature on that interface to allow PIX2 to respond to ARP requests that HOST2 will generate.
You can do a static one-to-one xlate if there are fewer hosts than the PIX2-HOST2 subnet can contain, or do a many-to-one xlate if you want HOST2 to see all clients as coming from the same IP address.
To take the simplest case, using the one-to-one static code this on PIX2:
sysopt proxyarp inside - assumes HOST2 is off of inside interface
static (outside, inside) a.b.c.d w.x.y.z netmask 255.255.255.255 where x.z.y.z is the address of HOST1 as seen by PIX2 on the outside interface, and a.b.c.d is an address on the PIX2-HOST2 subnet and is the address that HOST2 will see HOST1 as.
Let me know if this helps.