AN EASY WAY TO KNIT 
A LARGER SIZE THAN THE PATTERN OFFERS
Consider simply changing to a bulkier yarn and a larger stitch size. Most bulky machines  will handle the low end of #5 yarn [aka chunky, bulky] at the top stitch sizes and get a  gauge of about 3.5 stitches per inch. A yarn I have used successfully in this weight range  on knitting machines is Northlands Timbers, from Herrschnerr's. Changing to such a yarn  and following a pattern that was designed for a gauge of 4 stitches/inch will make the  final product 1.14 times the size given in the pattern. It will also be proportionately  longer.

The same principle is at work if, using a standard gauge machine, you select a yarn that knits at 6.5 rather than 7 stitches per inch. The new gauge will make the resulting garment 1.07 times the stated size. If the largest size at the original gauge is 50", it changes to 53" at the replacement gauge. 

Using my Bulky Cardi-kets book as an example, the original largest sizes are Waterfall=54", Cabled Classic=46", Cross Bred Cardi=48, Fancy Threads=51", New Di-rection=58", Notch Collar Cardi=51", Greek Key Coat-52", Bonus Blouse=52", Winter  Cheer=46" [for this explanation I have dropped values beyond the decimal point.]
If you make this simple change, the largest size possible for each pattern in my Bulky Cardi-kets bookis as  follows  Waterfall=62", Cabled Classic=53", Cross Bred Cardi=55, Fancy Threads=58", New Di-  rection=58", Notch Collar Cardi=59", Greek Key Coat-59", Bonus Blouse=61", Winter  Cheer=52". Opera Wrap cannot be enlarged using this method. 
You may find that you don't actually require the largest size so, to predict how a particu-lar size will turn out if bulkier yarn is used, multiply the size given in the pattern by 1.14.  The result is the expected measurement using thicker yarn. Of course, you don't have to  use yarn that is maximally bulky. If a yarn that gets 3.75 stitches/ inch is used instead.  the result is 1.066 times the original size. A quarter of a stitch per inch is not a very noticeable change in the gauge but can make quite a difference to fit. A few yarns at the  very top of the number 4 range get this gauge. It would make the largest possible size  for each pattern:  Waterfall=58", Cabled Classic=50", Cross Bred Cardi=52, Fancy Threads=54", New Direction=54", Notch Collar Cardi=57", Greek Key Coat-59.