How to use scriptmanager with existing javascript

Hi Friends
I have an existing site having a bulk of javascript used on the page.
Now the page has to convert in AJAX but while using update panel my controls are not able to use existing javascript
It is not feasible to use ScriptManager.RegisterClientScriptBlock because script is around 200 to 300 of lines and also not feasible to move it in another JS File and Use ScriptManager.RegisterClientScriptInclude since each page has different script with almost same numbers of line
Is there any way so that i can use existing script with minimum number of steps with full reusability


Thanks 
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