You're correct that the RV042 router's implementation of SSL is weak.
Stepping back, why do you need an SSL key on your router? Assuming there's a good reason that can't be met via other techniques, can you implement a compensating control (such as an ACL) to mitigate the risk and thus meet that compliance requirements?
If not, then you would need to move the function to a more secure device - the new ASA 5506 might be one such candidate. Your local Cisco partner should be able to help you with product selection based on a more in-depth analysis of your environment and requirements