VLAN port to another switch

[MSR63]

I have a VLAN with 4 ports at a data center, 1 is open - Wondering if it would be possible to add the 4th member to that VLAN, however it would be located at a remote site. Perhaps – be just a one-node VLAN itself; then it would go through a separate VPN to our data center, into a separate VPN there, and then – somehow – join the other 3 connections in that VLAN?

At the DataCenter - I have an ASA with an extra port, subnet 10.1.5.x and at the remote site I have a PIX with an extra port, subnet 10.2.5.x

Both subnets are the same domain.

Any suggestions or is it just wishfull thinking?