Yes. The only way I know to do it is by using some VBA code. Are you familiar with VBA programming? If so, the short answer is...
1. You want to open Form1 in DB1 from DB2
1. Open DB2
2. Add a reference to DB1 in Tools/References of DB2.
3. Add a module in DB1 that opens Form1
4. In DB2 call the procedure you created in DB1 to open Form1.
If this is something you think would be useful to you I can provide more details. My experience has been, once you start referencing other databases within a database the number of crashes you experience will increase.
I have a database that is nothing but code that is used by all my databases. If I have a database open that references this database, then I try to open the code database, both databases will crash. It's more of a nuisance for me since I am the programmer and the user. But if you plan to implement this for a customer it may not be as stable as you might like. I am not trying to scare you, I use this scheme everyday, but it is something to consider.