Storing Troops

[Roman]

Is there anyway to store spare troops besides in castles? I currently have a human-based army: Paladins, Knights, Horsemen, Inquisitors, Rune Mages, Royal Griffins and a Green Dragon (including troops in reserve). It is a really good army, but I would like to try my hand at an orc-based army a dwarf-based army or even a dinosaur-based army. Still, I want to preserve my old army, which I have invested a lot into, so I am unwilling to dismiss any troops and cannot store any more troops in the castles available to me (these do hold some orc-stacks, for example, so I will be able to swap some troops for that, but I would like to try a dwarf-based army before an orc-based one, since I now have access to Montero). Conquering more castles is a long way off (they are well protected), so I am wondering if there are any other options. Thanks for any advice!