If the end goal is to segregate IP traffic and routing between different environments within the same device, you can do it using a combination of partitions an route domains.
That would allow you to segregate traffic within the same LTM instance.
You can do this by:
Create a new partition
Moving to the partition you just created
Create the vlans within the new partition
Create a new route domain (selecting strict isolation, the vlans you just created for the partition, and making it the default route domain for the partition)
Create the self IPs for the vlans
You repeat the process for each partition you want to create.
Make sure you assign a different route domain ID for each partition you create.
If you're doing an HA pair you need to do this on each box.
Make sure you use the same names for the vlans, route domains and partitions on each box.
Once both boxes have the same partitions, vlans, route domains and self IPs, you can create the object that get synchronized with the device group on the Active box. Ex. Floating IPs, default routes, pools, profiles, iRules, virtual servers, etc.
This setup allows you to keep traffic from one partition isolated from the rest. Thus you can have a different default route for each partition, which is a great convenience.
Hope this helps!