I don't think you will be able to that with simple CSS.
You don't want to change your java code for an aesthetic issue but, the problem is that your table really shouldn't have a changing number of columns. The parameters columns should be only one column with some other means to separate the values. You could generate a comma separated list of the parameters in the second column. That way you would always have 3 columns and the thing will be far easier to format properly.
If you really want to keep the values in separate columns, you should use the colspan attribute on the last parameter. For example the last parameter column could look like this, with in your java string (or whatever you use to generate the html) looking somewhat like :
"<td colspan="+ (maxNumberOfColumns-currentColumnIndex) +">"
I strongly suggest you adjust you java code to do this, as the alternatives (modifying with javascript) are a lot more painful (even with things like JQuery).