I would like to direct users to a visualforce page that clones the opportunity AFTER they choose a record type. 

Is there a way that I can rewrite the button code to somehow "detour" to the opportunity record type selection page prior to going to the vf page? 

/apex/addstudyED?id={!Opportunity.Id}

OR  

Can i somehow add code to the controller that will allow the user to stop at the record type selection page?

public class AddSTudyEDController {

//added an instance varaible for the standard controller
private ApexPages.StandardController controller {get; set;}
// add the instance for the variables being passed by id on the url
private Opportunity o {get;set;}
// set the id of the record that is created -- ONLY USED BY THE TEST CLASS
public ID newRecordId {get;set;}

// initialize the controller
public AddStudyEDController(ApexPages.StandardController controller) {

//initialize the stanrdard controller
this.controller = controller;
// load the current record
o = (Opportunity)controller.getRecord();

}

// method called from the VF's action attribute to clone the po
public PageReference AddStudyED() {

// setup the save point for rollback
Savepoint sp = Database.setSavepoint();
Opportunity newO;


try {

//copy the purchase order - ONLY INCLUDE THE FIELDS YOU WANT TO CLONE
o = [select Id, RFI__c,Molecule_Size__c, Name,AccountId, Parent_Opportunity__r.Record_Type_Name__c,Parent_Opportunity__c,Compound_Name__c, Compound__r.Id, StageName, Currency_To_Quote__c,CloseDate, Program_Managed__c,Integrated_Opportunity2__c,funding_approved__c from Opportunity where id = :o.id];
newO = o.clone(false);

if(o.Parent_Opportunity__c==null)
newo.Parent_Opportunity__c = o.Id;

if(o.Parent_Opportunity__r.Record_Type_Name__c=='ED - ADMIN TEST'
||o.Parent_Opportunity__r.Record_Type_Name__c=='BIOA'
||o.Parent_Opportunity__r.Record_Type_Name__c=='TOX'
||o.Parent_Opportunity__r.Record_Type_Name__c=='BIOTECH'
||o.Parent_Opportunity__r.Record_Type_Name__c=='DM'
||o.Parent_Opportunity__r.Record_Type_Name__c=='CMC')
newo.Parent_Opportunity__c = o.Parent_Opportunity__c;

if(o.Parent_Opportunity__r.Record_Type_Name__c!='ED - ADMIN TEST'
&&o.Parent_Opportunity__r.Record_Type_Name__c!='BIOA'
&&o.Parent_Opportunity__r.Record_Type_Name__c!='TOX'
&&o.Parent_Opportunity__r.Record_Type_Name__c!='BIOTECH'
&&o.Parent_Opportunity__r.Record_Type_Name__c!='DM'
&&o.Parent_Opportunity__r.Record_Type_Name__c!='CMC')
newo.Parent_Opportunity__c = o.id;


newo.Name = 'pending - must overwrite';
newo.Stagename = 'Prospect';


insert newO;

// set the id of the new po created for testing
newRecordId = newO.id;

// copy over the line items - ONLY INCLUDE THE FIELDS YOU WANT TO CLONE
List<OpportunityContactRole> items = new List<OpportunityContactRole>();
for (OpportunityContactRole cr : [Select r.Id, r.ContactId, r.OpportunityId, r.IsPrimary, r.role From OpportunityContactRole r where OpportunityId = :o.id]) {
OpportunityContactRole newcr = cr.clone(false);
newcr.OpportunityId = newO.id;
items.add(newcr);
}


// copy over the line items - ONLY INCLUDE THE FIELDS YOU WANT TO CLONE
List<OpportunityTeamMember> teams = new List<OpportunityTeamMember>();
for (OpportunityTeamMember tm : [Select m.Id, m.OpportunityAccessLevel, m.OpportunityId, m.UserId, m.IsDeleted, m.TeamMemberRole From OpportunityTeamMember m where OpportunityId = :o.id]) {
OpportunityTeamMember newtm = tm.clone(false);
newtm.OpportunityId = newO.id;
teams.add(newtm);
}
insert items;
insert teams;

} catch (Exception e){
// roll everything back in case of error
Database.rollback(sp);
ApexPages.addMessages(e);
return null;
}

return new PageReference('/'+newO.id+'/e?retURL='+O.id+'&saveURL='+newO.id);
}

}