Support for other scripting tool

Looking at wpt code, I could not find a way to easily run manual tests, i.e. have the performance being measured on a browser started and stopped by hand. The reason why I would want to do that, is because we have a tool called iMacros (support for most browsers with plugin), which could be used together with wpt to monitor a whole complex script run. Ultimately if we found a way, we would prepare some ami to run imacros scripts.

A first step in that direction would be to be able to test manually running such scripts (which would behave exactly like running a manual session on a browser). So my question is: have I missed something or are my assumptions right that it would require substancial changes in wpt code? It looks like system wide injecting wpthook just is not enough, is it? If someone already did some work in that direction and could provide some input, I would also welcome any comment on this.

Thanks for reading.