When you talk about extended cubes (ie. linked) you're extending the entity hierarchy. However, extending cubes works in the opposite way of extending any other dimension. So where in the accounts, you'd extend Sales to more detailed accounts, it doesn't work the same way in Entities. To handle entering at Houston in LRP and HH/SH in Finance, I believe you won't be able to link cubes. You'll need to move data between the two cubes - either DM or connector rule.
Celvin you can also change the Adjustment Type on the accounts for a specific scenario type which will allow you to type into parent Entities. I've found that to be a good solution for specific scenarios which want to enter data into parent Entities.
The only thing to think about is it writes to O#AdjInput so it would no longer allow journal entries to that account/scenario type combination. But, that usually is OK for any LRP scenario as it won't utilize journal entries.
