Forms Authentication overrides impersonation in IIS7

I have been searching all over the place for a solution to this.

I have an AS开发者_Go百科P.NET app which ran fine on IIS6. On IIS 7.5 (Integrated pipeline) I am running into some problems. <identity impersonate="true" /> is set in the web.config as the app needs to access some resources under the IIS IUSR account. If works fine as when a user isn't logged in (i.e. the app impersonates IUSR and accesses the resources fine).

As soon as you logon via Forms Authentication (backed by a DB) impersonation stops working and it reverts to the app pool user identity (which doesn't have access to the required resources, I have verified this with procmon). I understand this is probably a limitation of Forms Authentication in integrated mode.

Is there any workaround which would let me impersonate IUSR while still using Forms Authentication?