What you want to do is part of the PDL (printer description langauge). IIRC the HP4000 supports 3 langauges. PCL5e, PCL 6 (or XL) and PostScript.
If you try to call these from lp, the escape sequence in the data will overwrite these setting (assuming the data file has formatting which is not always the case)
Do you know what PDL you are using?
Is your data formatted (PS/PCL) or raw (no escape sequnces)?
Can you do broune shell scripting?
From Solaris you can disable the queue, print the job you want and then view the spool file to see what the PDL is.