Hi qwazee,

I would suggest that your customer purchase a 50-hour rental license such as 6ES7823-1GE08-0YA5. I see no other option that meets the license conditions. Leasing of a license is not permitted under these conditions.

Here are some excerpts from the General License Conditions for Software Products for Automation and Drives (Status: January 31, 2019):

• 2.2 Floating License
  The Customer shall be granted a non-exclusive right, valid for an indefinite period of time, to use the Software simultaneously on such number of the Customer’s objects (e.g. users or devices) as specified in the Order Data and/or the CoL. The Customer is permitted to install the Software on up to ten (10) times as many Instances as it has acquired licenses for objects. Example: In case the Customer acquires the license to use the Software on three (3) objects at the same time, it is entitled to install the Software on thirty (30) of the Customer’s Instances.
• 2.4 Rental Floating License
  The Customer shall be granted the non-exclusive right, limited in time as stipulated in the Order Data or the CoL (see "Type of Use"), to use the Software simultaneously on such number of the Customer’s objects (e.g., users or devices) as specified in the Order Data or the CoL. For this purpose, the Customer is permitted to install the Software on up to ten (10) times as many of the Customer’s Instances. If the period of use is specified in hours, the calculation of the respective time limits for usage shall be determined from the Software start-up and end with the closing of the same. If the period of usage is specified in days, weeks or months, the specified period commencing with the first start-up of the Software shall apply regardless of actual usage. If the usage period is date-based, the license shall end on this date irrespective of actual usage.
• 5.1 The Customer shall have no right to rent out or in any other way license Software, or to publicly make it available or accessible by way of cable or wireless, or to make it available to third parties for any charge or free of charge, for example, in the course of application service providing or as "Software as a Service".
• 5.4 The Customer is entitled to transfer any Software acquired by the Customer in the course of a purchase from Siemens to a third party. In such case the Customer shall cease fully to use the Software and shall remove all installed copies of the Software from its equipment and its Instances and erase any copies located on other data medium or, at the request of Siemens, shall provide the same to Siemens insofar as the Customer is not required to retain the same for a longer period in accordance with applicable law. The use of any such retained copies is prohibited.
  

Kind regards
Stefan