Yes this is possible and can be achieved very easily.
Creation of .umt files is described in the SimGEN user manual, DGP00686AAA (SimREPLAYplus users should refer to DGP01074AAA, though for a more comprehensive discussion please go to the SimGEN manual). That section of the manual includes a description of "INTERP" (Interpolated motion) commands that can be entered at the start of the .umt file. It goes on to provide exactly the demonstration requested here - using the INTERP command to avoid having to enter timestamped records for every instance throughout a static period.
Attached are three files that describe the same, very simple vehicle motion, with a 2 minute static period at the start. The static period is created using the above explanation. To use any of these files directly please change the extension from .txt to .umt first. The .txt extension has been used so that clicking the file to open it from the knowledge base makes it easier to view.