Since I'm sure that many will jump in with the more complex and more-often-found hand-held remote solutions I thought that I suggest the trivial one first.
Way back when TMCC was introduced in order to take advantage of 135 Watt bricks for conventional operators they were also offered in conjunction with what was called a "PowerStation". This was/is a table-top throttle that when connected to a 135 brick makes a nice "transformer" set for traditional (non-command) operation.
Look for a 6-12938.
The problem is, in your situation, that a 6-12938 includes BOTH the throttle (PowerStation) and brick (PowerHouse 135). Since you already have the bricks you just need the throttles. They may be hard to find separately since they were never originally sold separately, only in together with a brick.
Having said this I have seen them available at a number of train shows over the last several years--in spite of the fact that they did not seem very popular in their day, or presently for that matter. (It appears to be the case that almost everyone bought bricks separately for command control, instead of together with PowerStations for conventional use.)