Ok, the solution is not as eloquent
as I had thought, but here we go, this can apply to any .vhd, not just page file, but it doesn't prevent doing the initial backup, just future changes, so this is probably not what you are looking for.
Exclude page file churns
To improve the performance of your Hyper-V backups, choose the option not to back up the entire churn in your pagefile. This gives you the benefit of reduced storage requirement and improvement in backup performance. Excluding pagefiles, DPM does not affect
replica creation and consistency check. The only change is that when the pagefile is excluded, DPM does not perform incremental backups on the pagefile. To exclude pagefiles, perform the following procedure:
1. Move the pagefile for a virtual machine to a different VHD.
2. Exclude pagefiles by using the Set-DPMGlobalProperty cmdlet. For more information about how to use this cmdlet, see Set-DPMGlobalProperty.
Names of pagefile VHDs that should be excluded from backup jobs for HyperV data source. Supports use of wildcards. Use commas to separate multiple VHD names.
Default Value none
Accept Pipeline Input? false
Accept Wildcard Characters? false
To exclude some page file VHDs
In this example, all VHDs protected on TestingServer that have names that end with _pagefile.vhd are marked for exclusion.
PS C:\> SetDPMGlobalProperty -DPMServerName TestingServer -HyperVPagefileExclusions "*_pagefile.vhd"
To add more page file VHD exclusions
In this example, VHD files that have mypgf in their name are added to the existing exclusion list.
PS C:\> SetDPMGlobalProperty -DPMServerName <DpmServer> -HyperVPagefileExclusions "*_pagefile.vhd,*mypgf*.vhd*"
To remove all page file VHD exclusions
In this example, all existing exclusions are removed.
PS C:\> SetDPMGlobalProperty -DPMServerName <DpmServer> -HyperVPagefileExclusions ""