I haven't done it in (Washington) for so long I really don't know how I would approach entering the data. I basically tell them that it is not going to save any tax and it's going to double the accounting fee (because I'd be doing two returns) and keep talking until I either talk them out of it, or they go somewhere else.
If there is a non tax reason they want to do it (ie trust issues) I just don't want to be involved in that anyway.
After following jeffmcpa 's steps then using a multi-column spreadsheet make your own chart of the income and w/h items in his and her and one/half columns. The totals of these columns will need to match finished return. Attach this spreadsheet as a pdf to return.
Enter w-2 etc for your taxpayer. Use the Other income line to increase or decrease income to match. The w/h total may have to be input at the lesser amount on a W-2 because a negative w/h does not work. It is a royal pain if they have to MFS. Good Luck.