How about instead of using the "host-only" network, try the following:
Step 1
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Add a 2nd Network Card (NIC) to each of your Hosts. NIC 1 of each Host plugs into your Production network, NIC 2 plugs into shared desktop network switch on your desk. Configure Workstation on each Host to bridge to NIC 2. Run your Guests in Bridged mode.
Now all of your Guests (on both of your Hosts) are on the same isolated network (let's call it the Lab network). Since you don't have a DHCP server on the Lab network you'll want to configure your guests with static IP addresses (or find a way to provide DHCP (see Step 2)).
Step 2
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In order to connect your Lab and Production networks you'll want to set up some sort of device to connect/route between them. You should include your IT department in this planning stage so they aren't "surprised" in the future.
In my opinion, the simplest solution would be to purchase a broadband router and plug it up between your Production network switch and your Lab network switch. Something like the Linksys BEFSR41 would do the trick. Broadband routers typically include DHCP servers and handle NAT translation, so things should "just work". (Also, if you purchase something like the BEFSR41 it includes a 4-port switch that you can use for Step 1. )
Alternatively, if you don't want to purchase additional hardware, you can set up a Guest with two virtual NICs. Bridge one of the virtual NICs to the Host NIC on the production network, and bridge the other virtual NICs to the Host NIC on the Lab network. Then install some sort of software in the Guest to route between the two, such as Microsoft's RRAS or something similar.
