HR Helpdesk pass parameter

Summary:

I wish to be able to navigate from a custom Page that's been defined within HR HD under a custom group (in the Structure area of HRHD), passing through the value of the category clicked through on to launch into creating a new service request. I've got everything working, bar passing through the category value. How are these coded in HRHD as parameters?

I have achieved this in B2C/Service/Rightnow before where I pass the value of category as c=153 etc. So was wondering if this is achievable in HRHD as well?