in the .bic file, in the tab general setting on the right side there is a slot that says start unit 2 which in default is the worker replace this with any "land" unit and you have the soulution, or if you have v1.29 and you make a .bic file to save as say a scenario then click on the rules tab and enable the custom player rules and then click the flag tab before all the helps "question marks" and then you can pick multiple units you want to start with and how many
hope this helps