You can't. To ask project not to use dates is like asking an accountancy
package not to show balances and $!!
However, you can format the timescale so that the labels show Month1, Month2
and Week1, Week2. In fact all my initial schedules always show this and the
first task is always Approval to proceed or customer signs order. That way I
always show how may weeks to complete AFTER the go ahead is given.