Motorola provide a tool called StartUpCtl, available from http://support.symbol.com/support/search.do?cmd=displayKC&docType=kc&externalId=13155&sliceId=&dialogID=41123441&stateId=0%200%2041121294 that will give you full control of what is launched at startup.
In order to make your RhoElemenst installation persist you'll need to use the persistent installer, which keeps a copy under \Application\ and reinstalls when necessary.
Thanks. I was actually able to figure it out by making a simple registry change:
; Load RhoElements on Startup [HKEY_LOCAL_MACHINE\Init] "Launch80"="\Program Files\RhoElements\RhoElements.exe"
For people who may read this in the future, simply place the above text in a .reg file and copy the file to the /Applications directory.
* Launch80 - the number following Launch is the order in which the application should load against any other startup apps. This value can be anything between 1 and 99.