Dear,
As you said, your user not interested to create P.R and wants to create SES directly.But to crte SES you need to have valid P.O in place.
In SAP we have option to create service entry sheet with unknown account assignment using maintenance plan.For this you need to have a Open purchase order with account assignment as "U" and item category as "D" for a particular period.
1) Create a Maintenance plan( Plan category as SES) and assign service P.O to the maintenance plan.
2) schedule it as per the service frequency, for example month end to capture miscellaneous maintenance service cost.
3) once service entry sheet is created you can create a maintenance order and assign it to SES.
This normally helps engineering department for known services at certain frequencies.Example: AMC for KILN PLC systems, so here we can have a open P.O and maintenance plan which triggers SES quarterly.So service engineer comes every quarter and does the service.So engineering person creates a maintenance order once service engineer comes to site and assigns the same to SES.Here system updates directly actual cost in to the maintenance order.
Hope this may help you.
Reagrds,
pardhu