It might be an idea to introduce your management to the concept of metrics. In the mean time, put in place the means of gathering the information required for the metrics.

This is a good way of turning a technical problem (having a programming language imposed on you) into business language that pointy haired bosses understand.

What I am talking about:

• Size of application: How many lines of code? How many pages of documentation? Estimated effort required for Java rewrite in man-days.
• Maintainability: How stable will the application be in Java? in Perl? If it ain't broken don't fix it. What is the Mean Time to Fix problems (mttf)? What is the cost of maintenance in terms of head count?
• Flexibility: How easy is it to add new functionality, and meet changing business requirements? How often do business requirements change? How much development-lag is there in each business driven enhancement?

You may find that this approach will help with whatever programming language you are using. It may help you get hard evidence that the company should stick with perl.