Hi,
You are right that .Net 4.5 is currently not supported. There is ER logged for this purposed which is available from the following link:
http://support.openview.hp.com/selfsolve/document/FID/DOCUMENTUM_QCCR1J31305
If you want you can review the following posts :
NET-Protocol-Recording-Best-Practices
LoadRunner Support Tip Getting Compilation error in Net script
If you want you can try to create a custom filter and give it a try if you want.
As a workaround you can try to record your application using RDP protocol.
Kind regards,