I went ahead and paid to opened a support case with Microsoft to try to work on this issue (as the issue is essentially the lack of ability to control the size of this WebCacheV01.dat file). They basically told me that there is absolutely no way to control the size of this cache. You'd think that they would provide a way to control this via a local policy or at least in IE being that Microsoft is all about granular control in products such as Group Policy.
I ended up coming up with a solution that works pretty well. If you deny each user permissions to their own Webcache folder, the browser simply doesn't write to cache. I left the player running like this with 250+ transactions for a few weeks without any trouble (transactions going unknown, etc). All you need to do is run the below script once after the player builds all user accounts. This way you don't need to keep running scripts to clean the cache.
icacls "C:\Users\SEUM-User-1\appdata\Local\Microsoft\Windows\WebCache" /deny "SEUM-User-1":(f) /t /c
icacls "C:\Users\SEUM-User-2\appdata\Local\Microsoft\Windows\WebCache" /deny "SEUM-User-2":(f) /t /c
icacls "C:\Users\SEUM-User-3\appdata\Local\Microsoft\Windows\WebCache" /deny "SEUM-User-3":(f) /t /c
icacls "C:\Users\SEUM-User-4\appdata\Local\Microsoft\Windows\WebCache" /deny "SEUM-User-4":(f) /t /c
icacls "C:\Users\SEUM-User-5\appdata\Local\Microsoft\Windows\WebCache" /deny "SEUM-User-5":(f) /t /c
icacls "C:\Users\SEUM-User-6\appdata\Local\Microsoft\Windows\WebCache" /deny "SEUM-User-6":(f) /t /c
icacls "C:\Users\SEUM-User-7\appdata\Local\Microsoft\Windows\WebCache" /deny "SEUM-User-7":(f) /t /c
Hopefully this can be of use.
Thanks,
Josiah