We don't use expenses, either, just resource assignments. Works well for us. There are 3 types of resources that can be assigned:
- Non labor and
We use each and for the non labor and material we do spread cost over the life of the activity. You do have the option to use the unit price (we don't) or just put in a lump sum. The cost will spread based on the cost curve.
In our case we created resources for each of our accounting expense codes (land, construction, OFM, others). I am not in front of P6 at the moment but we change the resource assignment settings to turn of cost calcs based on units. Works for us but we are looking at possibly reversing that setting. IOW, use the $1 for the unit price and then enter the cost of the item in Units. An advantage to this method is that it (maybe) makes it easier to use the manual curve to spread cost over time.
There are plenty of ways to spread cost over time.
One headache for us is that we do not accrue our cost BUT to help finance we can project cost for our General Ledger. (So an unfortunate attempt to complicate matters here) we have, for example, the work being completed in one month, knowing full well that the invoice and payment won't be processed till the next month or maybe later. We stagger a LOW activity to reflect this.