Another route is to approach an agency (elanit, talisman - pm me for more). They'll do your payroll for you and suggest contract routes to sort out the mess, (e.g. one from you to them employing an agency employee) and one from them to you (naming you as the employee).

They'll normalyl look to take between 50 and 100 CHF per day for this.

Its not cheap, but they'll do your payroll and sort it out. Its not an option I would recommend (I would go down the swiss gmbh route) but it is another option.