Adding A Column To VLDB 200GB Table

The column I'm adding needs to be part of the clustered PK (it will be the last of three columns) so I need to recreate all the indexes.

My DB is set for FULL recovery mode ALLOW_SNAPSHOT_ISOLATION ON. I've tried two methods so far.

Method 1:

BEGIN TRANSACTION
CREATE TABLE dbo.Tmp_copyoftablewithnewfield
(
) ON PRIMARY
IF EXISTS(SELECT * FROM dbo.originaltable)
EXEC('INSERT INTO dbo.Tmp_copyoftablewithnewfield (<original fields>)
SELECT <original fields> FROM dbo.originaltable WITH (HOLDLOCK TABLOCKX)')
GO
DROP TABLE dbo.originaltable
GO
EXECUTE sp_rename N'dbo.Tmp_copyoftablewithnewfield', N'originaltable',
'OBJECT'
GO
<recreate PK constraint>
<rebuild indexes>
COMMIT

Pro's: Lets me add the new field in the spot I'd like it (not a big deal)
Con's: Tons of wasted space and time. It took about 15 hours.

Method 2:
SET XACT_ABORT ON
GO
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
GO
BEGIN TRANSACTION
<drop PK constraint>
<drop indexes>

ALTER TABLE [dbo].[originaltable] ADD
[newfield] [tinyint] NOT NULL CONSTRAINT [DF_originaltable_newfield] DEFAULT
((1))

<recreate PK constraint>
<rebuild indexes>
COMMIT TRANSACTION

Pro's: No making a copy of the entire table taking up 200GB more space in the db data file
Con's: My tempdb grew to accomodate the row versioning info for every row in the 200GB table. It took over 30 hours.

A lot of time and disk space is wasted with both.

Since the db is going to be unavailable to users I have some flexibility here. I was considering turning ALLOW_SNAPSHOT_ISOLATION OFF and then trying method 2 again which should stop the versioning in tempdb and then turning it back on.

I was also curious if setting the database recovery mode to SIMPLE would cut down on db log usage and then I could set it back to FULL when done.

Do these really need to be in a transaction? If there's some hardware failure or something unexpected I can just restore from backup and do the conversion again. If the presence of the transaction itself is causing more disk usage for logging or any other slowdown, I think I'd rather do without.

Given the amount of time this conversion takes, I wanted to get some
feedback other than "just try it" before doing any new tests.

Thanks.